Patent Publication Number: US-11662112-B2

Title: Determination of stuck reversing valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/832,277 filed Mar. 27, 2020, by Amita Brahme et al., and entitled “DETERMINATION OF STUCK REVERSING VALVE,” which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to heating, ventilation, and air conditioning (HVAC) systems and methods of their use. In certain embodiments, the present disclosure relates to determination of a stuck reversing valve. 
     BACKGROUND 
     Heating, ventilation, and air conditioning (HVAC) systems are used to regulate environmental conditions within an enclosed space. Air is cooled or heated via heat transfer with refrigerant flowing through the system and returned to the enclosed space as conditioned air. In some cases, an HVAC system may be configured to operate as a heat pump. Such an HVAC system may include a reversing valve. The position of the reversing valve may be adjusted to reverse the flow of refrigerant through the HVAC system to operate according to a heating mode or a cooling mode. 
     SUMMARY OF THE DISCLOSURE 
     In an embodiment, an HVAC system includes a reversing valve configured to receive refrigerant and direct the received refrigerant based on an operating mode of the HVAC system. When the HVAC system is intended to operate in a cooling mode, the reversing valve is configured to direct the received refrigerant to an outdoor heat exchanger. When the HVAC system is intended to operate in a heating mode, the reversing valve is configured to direct the received refrigerant to an indoor heat exchanger. The HVAC system includes a sensor which measures a heat-exchanger temperature associated with the outdoor heat exchanger. A controller monitors an outdoor temperature and the heat-exchanger temperature. The controller compares the monitored outdoor temperature to the monitored heat-exchanger temperature. The controller determines whether the HVAC system is intended to operate in a cooling mode or heating mode. In response to determining that the heat-exchanger temperature is less than the outdoor temperature and that the HVAC system is intended to operate in the cooling mode, the controller determines that a first reversing-valve fault is detected, wherein the first reversing-valve fault is associated with the reversing valve being in the heating configuration when the HVAC system is intended to operate in the cooling mode. 
     In another embodiments, An HVAC system includes a reversing valve configured to receive compressed refrigerant and direct the refrigerant based on an operating mode of the HVAC system. When the HVAC system is intended to operate in a cooling mode, the reversing valve is configured to direct the received refrigerant to an outdoor heat exchanger. When the HVAC system is intended to operate in a heating mode, the reversing valve is configured to direct the received refrigerant to an indoor heat exchanger. One or more suction-side sensors measure suction-side properties associated with refrigerant provided to an inlet of the compressor. The suction-side properties comprise a suction-side temperature. One or more liquid-side sensors measure liquid-side properties associated with the refrigerant provided from an outlet of the compressor. The liquid-side properties comprise a liquid-side temperature. A controller monitors the suction-side temperature and liquid-side temperature. The controller determines whether the suction-side temperature is greater than the liquid-side temperature. If the suction-side temperature is greater than the liquid-side temperature, the reversing valve is determined to be in an equalizing configuration. The equalizing configuration corresponds to a configuration in which the refrigerant provided from the outlet of the compressor is directed to the inlet of the compressor without first being directed to other components of the HVAC system. 
     In some cases, an HVAC system may experience a fault (e.g., a malfunction of one or more components of the HVAC system, a loss of charge, or like). Conventional approaches to detecting an HVAC system fault generally rely on an individual recognizing a loss of system performance. For example, an occupant of an enclosed space being conditioned by an HVAC system may recognize that the space is not comfortable or is not reaching a desired temperature setpoint. Such approaches result in delayed detection of system faults, such that it may be too late to take efficient and effective corrective action once a fault is identified. For instance, by the time a fault is detected using conventional approaches, damage may have occurred to system components, resulting in a need for repairs which may be costly, complex, or even impossible. Furthermore, previous technology is generally not capable of determining that an HVAC system fault (e.g., associated with a loss of system performance) is caused by a malfunction of a reversing valve. Previous technology also fails to distinguish between different types of reversing valve malfunctions. 
     This disclosure provides technical solutions to problems of previous technology, including those described above, by facilitating the detection of an HVAC fault caused by a malfunctioning reversing valve and/or determining a type of reversing valve malfunction (e.g., whether caused by the valve being in the wrong position for heating or cooling, or caused by the valve being stuck in an equalizing configuration, as described in greater detail below). This disclosure encompasses the recognition that certain measurable properties associated with the HVAC system and/or the surrounding environment can be monitored to both detect a reversing valve malfunction and distinguish between different types of such malfunctions. For example, an outdoor temperature and a temperature associated with an outdoor heat exchanger can be monitored and used to detect a faulty reversing valve which is in the wrong position for providing the cooling or heating associated with the operating mode of the HVAC system, as described in greater detail below with respect to  FIGS.  1 A-B  and  FIG.  2   . As another example, suction-side properties (e.g., temperature and/or pressure measurements) and liquid-side properties (e.g., temperature and/or pressure measurements) can be monitored and used to detect a faulty reversing valve which is stuck in an equalizing configuration, as described in greater detail below with respect to  FIG.  1 C  and  FIG.  3   . As such, this disclosure may be integrated into a practical application by providing an improved controller of an HVAC system, which more effectively detects reversing valve faults and provides information regarding the type of fault, such that appropriate corrective actions may be taken before the HVAC system is damaged. Certain embodiments may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1 A  is a diagram of an example HVAC system configured to operate in a cooling mode with the reversing valve in a cooling configuration; 
         FIG.  1 B  is a diagram of an example HVAC system configured to operate in a heating mode with the reversing valve in a heating configuration; 
         FIG.  1 C  is a diagram of an example HVAC system with the reversing valve in an equalizing configuration; 
         FIG.  2    is a flowchart illustrating an example method of detecting a fault associated with the reversing valve of the HVAC system of  FIGS.  1 A-C ; 
         FIG.  3    is a flowchart illustrating an example method of detecting a fault associated with the reversing valve of the HVAC system of  FIGS.  1 A-C  being stuck in the equalizing configuration illustrated in  FIG.  1 C ; and 
         FIG.  4    is a diagram of the controller of the example HVAC system of  FIGS.  1 A-C . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure and its advantages are best understood by referring to  FIGS.  1 A through  4    of the drawings, like numerals being used for like and corresponding parts of the various drawings. 
     As described above, prior to this disclosure, there was a lack of tools for effectively detecting reversing valve-related faults of an HVAC system. The systems and methods described in this disclosure provide solutions to these problems by facilitating the detection of reversing valve-related faults based on comparisons of particular combinations of measured properties. For example, an outdoor temperature and a temperature associated with an outdoor heat exchanger can be monitored and used to detect that a reversing valve is in the wrong position for the operating mode of the HVAC system, as described in greater detail below with respect to  FIGS.  1 A-B  and  FIG.  2   . As another example, suction-side properties (e.g., temperatures and/or pressures) and liquid-side properties (e.g., temperatures and/or pressures) can be monitored and used to detect that a valve is stuck in an equalizing configuration, as described in greater detail below with respect to  FIG.  1 C  and  FIG.  3   . 
     As used in this disclosure a “suction-side property” refers to a property (e.g., a temperature or pressure) associated with refrigerant provided to an inlet of the compressor. For example, a suction-side property may be a temperature or pressure of refrigerant provided to a compressor of an HVAC system (e.g., refrigerant flowing into the inlet of the compressor or refrigerant flowing in conduit leading to the inlet of the compressor. As used in this disclosure, a “liquid-side property” refers to a property (e.g., a temperature or pressure) associated with refrigerant provided from an outlet of the compressor. For example, a liquid-side property may be a temperature or pressure of refrigerant provided from a compressor of an HVAC system (e.g., refrigerant flowing out of the outlet of the compressor or refrigerant flowing in conduit leading from the outlet of the compressor. 
     HVAC System 
       FIGS.  1 A-C  are schematic diagrams of an example HVAC system  100 . The HVAC system  100  conditions air for delivery to a conditioned space. The conditioned space may be, for example, a room, a house, an office building, a warehouse, or the like. The HVAC system  100  may be configured as shown in  FIGS.  1 A-C  or in any other suitable configuration. For example, the HVAC system  100  may include additional components or may omit one or more components shown in  FIG.  1   . The HVAC system  100  includes a refrigerant conduit subsystem  102 , a compressor  104 , an outdoor heat exchanger  112 , a heating expansion device  120 , a cooling expansion device  122 , an indoor heat exchanger  124 , a thermostat  134 , and a controller  142 . The controller  142  is configured to detect and diagnose a fault or malfunction of the reversing valve  110 . For example, the HVAC system  100  may be configured for the determination of whether a fault of the reversing valve  110  is: (1) associated with the reversing valve  110  being in the wrong configuration for a given operating mode  138  (e.g., with the reversing valve  110  being in the cooling configuration illustrated in  FIG.  1 A  when the HVAC system  100  is operating in a heating mode, or vice versa), or (2) associated with the reversing valve  110  being stuck in the equalizing configuration illustrated in  FIG.  1    (e.g., when a heating or cooling operating mode  138  is desired). 
     The refrigerant conduit subsystem  102  facilitates the movement of a refrigerant through the cooling cycle of  FIG.  1 A , the heating cycle of  FIG.  1 B , or the equalizing cycle of  FIG.  1 C , such that the refrigerant flows as illustrated by the dashed arrows. The refrigerant may be any acceptable refrigerant including, but not limited to, fluorocarbons (e.g. chlorofluorocarbons), ammonia, non-halogenated hydrocarbons (e.g. propane), hydroflurocarbons (e.g. R-410A), or any other suitable type of refrigerant. 
     The compressor  104  is coupled to the refrigerant conduit subsystem  102  and compresses (i.e., increases the pressure of) the refrigerant. The compressor  104  may be a variable speed or multi-stage compressor. A variable speed compressor is generally configured to operate at different speeds to increase the pressure of the refrigerant to keep the refrigerant moving along the refrigerant conduit subsystem  102 . If compressor  104  is a variable speed compressor, the speed of compressor  104  can be modified to adjust the cooling or heating capacity of the HVAC system  100 . Meanwhile, a multi-stage compressor may include multiple compressors, each configured to operate at a constant speed to increase the pressure of the refrigerant to keep the refrigerant moving along the refrigerant conduit subsystem  102 . In the multi-stage compressor configuration, one or more compressors can be turned on or off to adjust the cooling and/or heating capacity of the HVAC system  100 . 
     The compressor  104  is in signal communication with the controller  142  using a wired and/or wireless connection. The controller  142  provides commands or signals to control operation of the compressor  104  and/or receives signals from the compressor  104  corresponding to a status of the compressor  104 . For example, when the compressor  104  is a variable speed compressor, the controller  142  may provide a signal to control the compressor speed. When the compressor  104  is a multi-stage compressor, a signal from the controller  142  may provide an indication of the number of compressors to turn on and off to adjust the compressor  104  for a given cooling or heating capacity. The controller  142  may operate the compressor  104  in different modes  138  corresponding to a user request (e.g., for heating or cooling) and/or load conditions (e.g., the amount of cooling or heating requested by the thermostat  134 ). The controller  142  is described in greater detail below with respect to  FIG.  4   . 
     One or more suction-side sensors  106  is generally positioned and configured to measure suction-side properties  144  associated with refrigerant provided to an inlet of the compressor  104 . The suction-side properties  144  may include a suction-side temperature  144   a  (i.e., the temperature of refrigerant flowing into the compressor  104 ) and a suction-side pressure  144   b  (i.e., the pressure of refrigerant flowing into the compressor  104 ). The suction-side sensor(s)  106  may be located in, on, or near the inlet of the compressor  104  to measure properties of the refrigerant flowing into the compressor  104 . The suction-side sensor(s)  106  are in signal communication with the controller  142  via wired and/or wireless connection and are configured to provide the suction-side properties  144  to the controller  142 , as illustrated in  FIGS.  1 A-C . The suction-side properties  144  are generally provided as an electronic signal that is interpretable by the controller  142 . For example, the suction-side sensor(s)  106  may provide an indication of the suction-side properties  144  (e.g., a current or voltage proportional to the measured suction-side properties  144 ) or may provide a signal which may be used by the controller  142  to calculate the suction-side properties  144 . The examples of  FIGS.  1 A-C  illustrate the suction-side sensor(s)  106  positioned in the refrigerant conduit subsystem  102  proximate to the inlet of the compressor  104 . However, it should be understood that the suction-side sensor(s)  106  may be positioned in any other appropriate position (e.g., in the inlet of the compressor  104  or further upstream of the inlet of the compressor  104 ). 
     One or more liquid-side sensors  108  are generally positioned and configured to measure a liquid-side properties  146  associated with refrigerant provided from an outlet of the compressor  104 . The liquid-side properties  146  may include a liquid-side temperature  146   a  (i.e., the temperature of refrigerant flowing out of the compressor  104 ) and a liquid-side pressure  146   b  (i.e., the pressure of refrigerant flowing out of the compressor  104 ). The liquid-side sensor(s)  108  may be located in, on, or near the outlet of the compressor  104  to measure properties of the refrigerant flowing out of the compressor  104  (e.g., in a compressed, liquid form). The liquid-side sensor(s)  108  are in signal communication with the controller  142  via wired and/or wireless connection and are configured to provide the liquid-side property  146  to the controller  142 , as illustrated in  FIGS.  1 A-C . Similarly to the suction-side properties  144 , the liquid-side properties  146  is generally provided as an electronic signal that is interpretable by the controller  142 . For example, the liquid-side sensor(s)  108  may provide an indication of the liquid-side property  146  (e.g., a current or voltage proportional to the measured liquid-side property  146 ) or may provide a signal which may be used by the controller  142  to calculate the liquid-side property  146 . The examples of  FIGS.  1 A-C  illustrate the liquid-side sensor(s)  108  positioned in the refrigerant conduit subsystem  102  proximate to the outlet of the compressor  104 . However, it should be understood that the liquid-side sensor(s)  108  may be positioned in any other appropriate position (e.g., in the outlet of the compressor  104  or further downstream from the outlet of the compressor  104 ). For instance, in some embodiments, the liquid-side sensor(s)  108  is located nearer the inlet of the outdoor heat exchanger  112 . 
     The reversing valve  110  is fluidically connected to the compressor  104 , outdoor heat exchanger  112  and indoor heat exchanger  124 . The reversing valve  110  is generally any valve which may be adjusted to the different configurations illustrated in  FIGS.  1 A-C . The reversing valve  110  facilitates operation of the HVAC system  100  as a heat pump to provide cooling to the conditioned space in the configuration illustrated in  FIG.  1 A  and heating to the conditioned space in the configuration illustrated in  FIG.  1 B . In  FIG.  1 A , the reversing valve  110  is in a cooling configuration for operating the HVAC system  100  in a cooling operating mode  138 . In  FIG.  1 B , the reversing valve  110  is in a heating configuration for operating the HVAC system  100  in a heating operating mode  138 . In  FIG.  1 C , the reversing valve  110  is in an equalizing configuration where refrigerant from the outlet of compressor  104  is routed to the inlet of the compressor  104  without passing through other components of the HVAC system  100  that are associated with the refrigeration cycle (i.e., the outdoor heat exchanger  112 , expansion valve(s)  120 ,  122 , and indoor heat exchanger  124 ). 
     The outdoor heat exchanger  112  is configured to facilitate movement of the refrigerant through the refrigerant conduit subsystem  102 . The outdoor heat exchanger  112  is generally configured to act as a condenser (e.g., to cool and condense refrigerant passing therethrough) when the HVAC system  100  is in the cooling configuration illustrated in  FIG.  1 A  and to act as an evaporator (e.g., to heat refrigerant passing therethrough) when the HVAC system  100  is in the heating configuration illustrated in  FIG.  1 B . The fan  114  is configured to move air  116  across the outdoor heat exchanger  112 . For example, the fan  114  may be configured to blow outside air through the outdoor heat exchanger  112  to help cool the refrigerant flowing therethrough for the cooling configuration of  FIG.  1 A  or to help heat the refrigerant flowing therethrough for the heating configuration of  FIG.  1 B . 
     One or more sensors  118  are generally located in, on, or near the outdoor heat exchanger  112  to measure a temperature  148  of the refrigerant associated with the outdoor heat exchanger  112 . In certain embodiments, sensor(s)  118  are positioned and configured to measure temperature(s)  148  of refrigerant flowing into, through, and/or out of the outdoor heat exchanger  112 . The sensor(s)  118  are in signal communication with the controller  142  using a wired and/or wireless connection and are configured to send measured temperature  148  to the controller  142 . For example, the sensor(s)  118  may provide a direct indication of the temperature  148  (e.g., a current or voltage proportional to the measured subcool value) or may be used by the controller  142  to calculate the temperature  148  (e.g., based on a signal provided by the sensor(s)  118 ). 
     When the reversing valve  110  is in the cooling configuration illustrated in  FIG.  1 A , refrigerant flows from the outdoor heat exchanger  112  toward a cooling expansion device  122 . In the cooling configuration of  FIG.  1 A , the heating expansion device  120  is generally maintained in a fully open position. The cooling expansion device  122  is coupled to the refrigerant conduit subsystem  102  downstream of the outdoor heat exchanger  112  and is configured to remove pressure from the refrigerant before the refrigerant is provided to the indoor heat exchanger  124 . Meanwhile, when the reversing valve  110  is in the heating configuration illustrated in  FIG.  1 B , refrigerant flows from the indoor heat exchanger  124  toward the heating expansion device  120 . In the heating configuration of  FIG.  1 B , the cooling expansion device  122  is generally maintained in a fully open position. The heating expansion device  120  is coupled to the refrigerant conduit subsystem  102  downstream of the indoor heat exchanger  124  and is configured to remove pressure from the refrigerant before the refrigerant is provided to the outdoor heat exchanger  112 . When the reversing valve  110  is in the equalizing configuration of  FIG.  1 C , refrigerant generally does not flow through the portions of the refrigerant conduit subsystem  102  that are fluidically connected to the outdoor heat exchanger  112  and the indoor heat exchanger  124 . 
     In general, each of the heating expansion device and the cooling expansion device  122  may be a valve such as an expansion valve or a flow control valve (e.g., a thermostatic expansion valve (TXV)) or any other suitable valve for removing pressure from the refrigerant while, optionally, providing control of the rate of flow of the refrigerant. Each of the heating expansion device  120  and the cooling expansion device  122  may be in communication with the controller  142  (e.g., via wired and/or wireless communication) to receive control signals for opening and/or closing associated valves and/or provide flow measurement signals corresponding to the rate of refrigerant flowing through the refrigerant subsystem  102 . 
     The outdoor heat exchanger  124  is generally any heat exchanger configured to provide heat transfer between air flowing through the outdoor heat exchanger  124  (i.e., contacting an outer surface of one or more coils of the outdoor heat exchanger  124 ) and refrigerant passing through the interior of the outdoor heat exchanger  124 . The outdoor heat exchanger  124  is fluidically connected to the compressor  104 , such that refrigerant flows in the cooling configuration of  FIG.  1 A  from the indoor heat exchanger  124  to the compressor  104  via the reversing valve  110  (see dashed arrows in  FIG.  1 A ). In the heating configuration of  FIG.  1 B , refrigerant flows, via the reversing valve  110 , from the compressor  104  to the indoor heat exchanger  124  (see dashed arrows in  FIG.  1 B ). A blower  126  causes return air  128  to move across the indoor heat exchanger  124 , such that heat transfer occurs between refrigerant passing through the indoor heat exchanger  124  and the flow of air  128 . The blower  126  directs the resulting conditioned air  130  into the conditioned space. In the cooling configuration of  FIG.  1 A , the return air  128  is cooled by the indoor heat exchanger  124  and provided to the conditioned space as a cooled conditioned air  130 . In the heating configuration of  FIG.  1 B , the return air  128  is heated by the indoor heat exchanger  124  and provided to the conditioned space as heated conditioned air  130 . The blower  126  is any mechanism for providing a flow of air through the HVAC system  100 . For example, the blower  126  may be a constant-speed or variable-speed circulation blower or fan. Examples of a variable-speed blower include, but are not limited to, belt-drive blowers controlled by inverters, direct-drive blowers with electronic commuted motors (ECM), or any other suitable types of blowers. The blower  126  is in signal communication with the controller  142  using any suitable type of wired and/or wireless connection. The controller  142  is configured to provide commands or signals to the blower  126  to control its operation. For example, the controller  142  may be configured to signal(s) to the blower  126  to control the speed of the blower  126  and/or to receive signals associated with a speed and/or status of the blower  126 . 
     The HVAC system  100  includes one or more outdoor temperature sensors  132  in signal communication with the controller  142 . The outdoor temperature sensor(s)  132  provide an outdoor temperature  150  to the controller  142 . The outdoor temperature  150  is generally provided as an electronic signal that is interpretable by the controller  142 . For example, the outdoor temperature sensor(s)  132  may provide an indication of the outdoor temperature  150  (e.g., a current or voltage proportional to the measured outdoor temperature  150 ) or may provide a signal which may be used by the controller  142  to calculate the outdoor temperature  150 . In some embodiments, the outdoor temperature  150  may be provided and/or determined from information provided by a weather data source  133 . For example, the weather data source  133  may provide current and/or forecast weather information, which includes historical, current, and/or forecast measurements of the outdoor temperature  150 . The HVAC system  100  may include one or more additional sensors (not shown for clarity and conciseness) to measure other properties of the conditioned space, the HVAC system  100 , and/or the surrounding environment. These sensors may include any suitable sensor positioned and configured to measure air temperature and/or any other property(ies) of the conditioned space, the HVAC system  100 , and/or the surrounding environment. 
     The HVAC system  100  includes one or more thermostats  134 , for example located within the conditioned space (e.g. a room or building). The thermostat  134  is generally in signal communication with the controller  142  using any suitable type of wired and/or wireless communications. The thermostat  134  may be a single-stage thermostat, a multi-stage thermostat, or any suitable type of thermostat. The thermostat  134  is configured to allow a user to input a desired temperature or temperature setpoint  136  for a designated space or zone such as a room in the conditioned space. The controller  142  may use information from the thermostat  134  such as the temperature setpoint  136  for controlling the compressor  104 , the reversing valve  110 , the fan  114 , and/or the blower  126 . 
     The thermostat may provide for display and/or input of an operating mode  138  of the HVAC system  100 . For example, the operating mode  138  may be a cooling operating mode or a heating operating mode. For instance, when the operating mode  138  is a cooling operating mode, the reversing valve  110  should be configured such that the flow of refrigerant proceeds through the refrigerant conduit subsystem  102  according to the cooling configuration of  FIG.  1 A . When the operating mode  138  is a heating operating mode, the reversing valve  110  should be configured such that the flow of refrigerant proceeds through the refrigerant conduit subsystem  102  according to the heating configuration of  FIG.  1 B . As described elsewhere in this disclosure, in some cases, the reversing valve  110  may malfunction such that the actual configuration of the HVAC system  100  (i.e., as illustrated in  FIGS.  1 A-C ), may not correspond to the operating mode  138  of the HVAV system  100 . For example, the thermostat  134  may indicate that the HVAC system  100  should be operating in a cooling mode  138 , but the reversing valve  110  may be incorrectly positioned such that refrigerant flows according to the heating configuration of  FIG.  1 B  or the equalizing configuration of  FIG.  1 C . As described in greater detail below with respect to  FIGS.  2  and  3   , the controller  142  is configured to determine if such a malfunction of the reversing valve  110  has occurred and distinguish between types of malfunctions of the valve  110 . 
     In some embodiments, the thermostat  134  includes a user interface for displaying information related to the operation and/or status of the HVAC system  100 . For example, the user interface may display operational, diagnostic, and/or status messages and provide a visual interface that allows at least one of an installer, a user, a support entity, and a service provider to perform actions with respect to the HVAC system  100 . For example, the user interface may provide for input of the temperature setpoint  136 , display and/or input of the mode  138 , and display of any fault alerts  140  related to the status and/or operation of the HVAC system  100 . A fault alert  140  may be associated with a determination that the reversing valve  110  is not in an appropriate configuration for a given mode  138 , as described above and in greater detail below with respect to  FIGS.  2  and  3   . 
     As described in greater detail below, the controller  142  is configured to (1) store measurements of the suction-side properties  144 , liquid-side properties  146 , heat exchanger temperature  148 , and outdoor temperature  150 ; (2) use this information to detect and diagnose a fault of the reversing valve  110 ; and (3) provide an appropriate fault alert  140 . For instance, in some embodiments, the controller  142  monitors the heat exchanger temperature  148  and outdoor temperature  150  and uses this information to detect and diagnose a malfunction of the reversing valve  110  (e.g., to detect when the reversing valve  110  is in the wrong position for providing heating or cooling as described in greater detail below with respect to  FIG.  2   ). In some embodiments, the controller  142  monitors the suction-side properties  144  and liquid-side properties  146  and uses this information to detect and diagnose a malfunction of the reversing valve  110  (e.g., to detect when the reversing valve  110  is stuck in the equalizing position associated with the configuration illustrated in  FIG.  1 C , as described in greater detail below with respect to  FIG.  3   ). The controller  142  is described in greater detail below with respect to  FIG.  4   . 
     As described above, in certain embodiments, connections between various components of the HVAC system  100  are wired. For example, conventional cable and contacts may be used to couple the controller  142  to the various components of the HVAC system  100 , including, the compressor  104 , sensors  106 ,  108 ,  118 ,  132 , the reversing valve  110 , the fan  114 , the blower  126 , and thermostat(s)  134 . In some embodiments, a wireless connection is employed to provide at least some of the connections between components of the HVAC system  100 . In some embodiments, a data bus couples various components of the HVAC system  100  together such that data is communicated therebetween. In a typical embodiment, the data bus may include, for example, any combination of hardware, software embedded in a computer readable medium, or encoded logic incorporated in hardware or otherwise stored (e.g., firmware) to couple components of HVAC system  100  to each other. As an example and not by way of limitation, the data bus may include an Accelerated Graphics Port (AGP) or other graphics bus, a Controller Area Network (CAN) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus, or any other suitable bus or a combination of two or more of these. In various embodiments, the data bus may include any number, type, or configuration of data buses, where appropriate. In certain embodiments, one or more data buses (which may each include an address bus and a data bus) may couple the controller  142  to other components of the HVAC system  100 . 
     In an example operation of HVAC system  100 , the system  100  starts up to provide cooling to an enclosed space. For example, the controller  142  may determine whether to operate in the cooling configuration of  FIG.  1 A  or the heating configuration of  FIG.  1 B  based on the current operating mode  138  and a comparison of an indoor temperature to the temperature setpoint  136 . For instance, if a cooling operating mode  138  is indicated and the indoor temperature is greater than the temperature setpoint  136 , the controller  142  may request that the reversing valve  110  be adjusted to the cooling configuration of  FIG.  1 A , and the compressor  104 , fan  114 , and blower  126  may begin operating to provide cooled conditioned air  130  to the space. Likewise, if a heating operating mode  138  is indicated and the indoor temperature is less than the temperature setpoint  136 , the controller  142  may request that the reversing valve  110  be adjusted to the heating configuration of  FIG.  1 B , and the compressor  104 , fan  114 , and blower  126  may begin operating to provide heated conditioned air  130  to the space. 
     If the reversing valve  110  is not operating as intended (e.g., is experiencing a fault or malfunction), the reversing valve  110  may be in an incorrect configuration for achieving cooling or heating. In order to detect such a malfunction and determine the type of malfunction (i.e., whether the reversing valve is in the wrong configuration for heating or cooling or if the reversing valve  110  is stuck in the equalizing configuration of  FIG.  1 C ), the controller  142  monitors the suction-side properties  144 , liquid-side properties  146 , heat exchanger temperature  148 , and outdoor temperature  150  and uses this information to detect a fault and provide a corresponding fault alert  140 . The controller  142  may further stop operation of the HVAC system  100  (e.g., by shutting down the compressor  104 , fan  114 , and/or blower  126 ), such that damage to the HVAC system  100  and/or unnecessary expenditure of energy is prevented before the fault or malfunction of the reversing valve  110  is corrected. 
     For example, the controller  142  may compare values of the heat exchanger temperature  148  and outdoor temperature  150  in order to detect a first example valve-fault scenario where the reversing valve  110  is in the heating configuration of  FIG.  1 B  when a cooling operating mode  138  is indicated by thermostat  134 . For instance, if a cooling operating mode  138  is indicated and the controller  142  detects that the heat exchanger temperature  148  is less than the outdoor temperature, then a fault of the reversing valve  110  is detected and a corresponding alert  140  is provided. A similar approach may be used to detect a second example scenario where the reversing valve  110  is in the cooling configuration of  FIG.  1 B  when a heating operating mode  138  is indicated. In this second scenario, a fault is detected and reported if a heating operating mode  138  is indicated and the heat exchanger temperature  148  is greater than the outdoor temperature  150 . The determination of faults associated with these first and second example scenarios is described in greater detail below with respect to  FIG.  2   . 
     The controller  142  may monitor values of the suction-side properties  144  and liquid-side properties  146  in order to detect a third example scenario where the reversing valve  110  is stuck in the equalizing configuration of  FIG.  1 C . In the equalizing configuration of  FIG.  1 C , rather than passing refrigerant through the refrigeration cycle (e.g., either for heating or cooling) associated with the outdoor heat exchanger  112 , expansion devices  120 ,  122 , and indoor heat exchanger  124 , the refrigerant provided from the outlet of the compressor  104  is directed to the inlet of the compressor  104 . For example, the controller  142  may determine that a suction-side temperature  144   a  is greater than a liquid-side temperature  146   a  and, in response, determine that the reversing valve  110  is stuck in the equalizing configuration of  FIG.  1 C . As another example, the controller  142  may determine that a ratio of a liquid-side pressure  146   b  to a suction-side pressure  144   b  is less than a threshold value. For example, the threshold value may be 1.2. In response, the controller may determine whether the suction-side temperature  144   a  has an increasing trend. If both the ratio of the liquid-side pressure  146   b  to the suction-side pressure  144   b  is less than the threshold value and the suction-side temperature  144   a  has an increasing trend, the controller  142  may determine that the reversing valve  110  is stuck in the equalizing configuration of  FIG.  1 C . Detection and diagnosis of the reversing valve  110  being stuck in the equalizing configuration of  FIG.  1 C  is described in greater detail below with respect to  FIG.  3   . 
     Example Method of Detecting a Reversing Valve Fault 
       FIG.  2    is a flowchart of an example method  200  of operating the HVAC system  100  of  FIGS.  1 A-C  for detection a fault of the reversing valve  110 . The method  200  facilitates the detecting and diagnosis of a fault of the reversing valve  110  in which the valve  110  is in the wrong configuration for a desired mode  138 . For example, the method  200  may be used to detect that the reversing valve  110  is configured in the cooling configuration of  FIG.  1 A  when a heating operating mode  138  is indicated by the thermostat  134 , and/or that the reversing valve  110  is configured according to the heating configuration of  FIG.  1 B  when a cooling operating mode  138  is indicated by the thermostat  134 . 
     Method  200  may begin at step  202  where the outdoor temperature  150  is monitored. For example, the controller  142  may receive the outdoor temperature  150  from the outdoor temperature sensor(s)  132  and/or the weather data source  133  intermittently (e.g., several times per second, each second, or the like) and store measurements of the outdoor temperature  150 . At step  204 , the heat exchanger temperature  148  is monitored. For example, the controller  142  may receive the heat exchanger temperature  148  from the heat exchanger temperature sensor(s)  118  intermittently (e.g., several times per second, each second, or the like) and store measurements of the heat exchanger temperature  148 . 
     At step  206 , the controller  142  determines whether the heat exchanger temperature  148  is less than the outdoor temperature  150 . For example, the controller may determine a difference between the heat exchanger temperature  148  and the outdoor temperature  150 . If this difference is less than zero, the controller  142  may determine that the heat exchanger temperature  148  is less than the outdoor temperature  150 . In some embodiments, the difference may be compared to a threshold value (e.g., a threshold of the thresholds  408  described with respect to  FIG.  4    below), and, in order for the heat exchanger temperature  148  to be considered less than the outdoor temperature  150 , the difference must be less than (e.g., more negative than) the threshold value. In some embodiments, the criteria of step  206  must be satisfied for at least a minimum time interval (e.g., of at least 30 seconds, e.g., of at least one minute, e.g., of at least five minutes) in order for the heat exchanger temperature  148  to be considered less than the outdoor temperature  150 . If, at step  206 , the heat exchanger temperature  148  is less than the outdoor temperature  150 , the controller  142  proceeds to step  208 . Otherwise, if the heat exchanger temperature  148  is not less than the outdoor temperature  150 , the controller  142  proceeds to step  218 . 
     At step  208 , the controller  142  determines whether the HVAC system  100  is set to a cooling operating mode  138 . As described above, during normal operation in a cooling operating mode  138 , the HVAC system should be configured according to the cooling configuration illustrated in  FIG.  1 A . If the HVAC system  100  is not set to a cooling operating mode  138 , then no fault or malfunction is detected, and the controller  142  returns to steps  202  and  204  to monitor the outdoor temperature  150  and the heat exchanger temperature  148 , respectively. However, if the HVAC system  100  is set to operate in a cooling operating mode  138  at step  208 , the controller  142  proceeds to step  210 . 
     At step  210 , the controller  142  determines that a reversing valve fault is detected. In some embodiments, prior to determining that the reversing valve fault is detected, the controller  142  first confirms that the HVAC system  100  is operating (e.g., that there is either a current heating or cooling demand). In other words, the controller  142  may confirm that the HVAC system  100  as a prerequisite to determining that the reversing valve fault is detected. In this example case, the controller  142  has detected that the relative values of the outdoor temperature  150  and the heat exchanger temperature  148  are inconsistent with normal operation of the HVAC system  100  in the cooling configuration illustrated in  FIG.  1 A  and that the HVAC system  100  is instead configured (incorrectly) according to the heating configuration of  FIG.  1 B . In other words, the reversing valve  110  is determined to be in the wrong position or configuration for providing cooling in the desired cooling operating mode  138 . 
     At step  212 , the controller  142  may test the responsiveness of the reversing valve  110 . This test may involve providing a signal to the reversing valve  110  which instructs the reversing valve  110  to change from the heating mode configuration of  FIG.  1 B  to the appropriate cooling mode configuration of  FIG.  1 A . Following provision of this test signal, the controller  142  may wait a predetermined time interval (e.g., 30 seconds, one minute, five minutes, or the like) before determining whether the criteria of steps  206  and  208  are still satisfied. If the criteria of steps  206  and  208  are still satisfied, the test fails, and the controller proceeds to step  214 . Otherwise, if the criteria of steps  206  and  208  are no longer satisfied, the controller  142  may determine that the reversing valve fault has been corrected. The controller  142  may still proceed to step  214  to report the detected fault such that inspection and/or appropriate preventative maintenance may be performed on the reversing valve  110 . 
     At step  214 , the controller  142  sends a reversing valve fault alert  140  for presentation on the thermostat  134 . For example, the fault alert  140  may indicate that the reversing valve  110  is in the heating configuration of  FIG.  1 B  rather than the appropriate cooling configuration of  FIG.  1 A  for the currently requested cooling operating mode  138 . In some embodiments, the alert  140  may also or alternatively be provided to a third-party (e.g., an administrator or maintenance provider of the HVAC system  100 ). This may facilitate the more rapid correction of the fault or malfunction of the reversing valve  110 . At step  216 , the controller  142  may stop operation of the HVAC system  100 . For example, the controller  142  may cause the compressor  104  to stop operating (e.g., to shut off). The controller  142  may also cause one or both of the fan  114  and the blower  126  stop operating (e.g., shut off). Stopping operation of the HVAC system  100  may prevent damage to the HVAC system  100 . 
     As described above, if, at step  206 , the heat exchanger temperature  148  is not less than the outdoor temperature  150 , the controller  142  proceeds to step  218 . At step  218 , the controller  142  determines whether the heat exchanger temperature  148  is greater than the outdoor temperature  150 . For example, the controller  142  may determine a difference between the heat exchanger temperature  148  and the outdoor temperature  150 . If this difference is greater than zero, the controller  142  may determine that the heat exchanger temperature  148  is greater than the outdoor temperature  150 . In some embodiments, the difference may be compared to a threshold value (e.g., a threshold of the thresholds  408  described with respect to  FIG.  4    below), and, in order for the heat exchanger temperature  148  to be considered greater than the outdoor temperature  150 , the difference must be greater than (e.g., more positive than) the threshold value. In some embodiments, the criteria of step  218  must be satisfied for at least a minimum time interval (e.g., of at least 30 seconds, e.g., of at least one minute, e.g., of at least five minutes) in order for the outdoor temperature  150  to be considered less than the outdoor temperature  150 . If, at step  218 , the heat exchanger temperature  148  is greater than the outdoor temperature  150 , the controller  142  proceeds to step  220 . Otherwise, if the heat exchanger temperature  148  is not greater than the outdoor temperature  150 , the controller  142  returns to steps  202  and  204  to monitor the outdoor temperature  150  and heat exchanger temperature  148 , respectively. 
     At step  220 , the controller  142  determines whether the HVAC system  100  is set to a heating operating mode  138 . As described above, during normal operation in a heating operating mode  138 , the HVAC system  100  should be configured according to the cooling configuration illustrated in  FIG.  1 B . If the HVAC system  100  is not set to a heating operating mode  138 , then no fault or malfunction is detected, and the controller  142  returns to steps  202  and  204  to monitor the outdoor temperature  150  and the heat exchanger temperature  148 , respectively. However, if the HVAC system  100  is set to operate in a heating operating mode  138  at step  220 , the controller  142  proceeds to step  210 . 
     As described above, at step  210 , the controller  142  determines that a reversing valve fault is detected. In this example case, the controller  142  has detected that the relative values of the outdoor temperature  150  and the heat exchanger temperature  148  are inconsistent with normal operation of the HVAC system  100  in the heating configuration illustrated in  FIG.  1 B  and that the HVAC system  100  is instead configured (incorrectly) according to the cooling configuration of  FIG.  1 A . In other words, the reversing valve  110  is determined to be in the wrong position or configuration for providing heating in the desired heating operating mode  138 . 
     As described above, at step  212 , the controller  142  may test the responsiveness of the reversing valve  110 . This test may involve providing a signal to the reversing valve  110  which instructs the reversing valve  110  to change from the cooling mode configuration of  FIG.  1 A  to the appropriate heating mode configuration of  FIG.  1 B . Following provision of this test signal, the controller  142  may wait a predetermined time interval (e.g., 30 seconds, one minute, five minutes, or the like) before determining whether the criteria of steps  218  and  220  are still satisfied. If the criteria of steps  218  and  220  are still satisfied, the test fails, and the controller  142  proceeds to step  214 . Otherwise, if the criteria of steps  218  and  220  are no longer satisfied, the controller  142  may determine that the reversing valve fault has been corrected. The controller  142  may still proceed to step  214  to report the detected fault such that inspection and/or appropriate preventative maintenance may be performed on the reversing valve  110 . 
     As described above, at step  214 , the controller  142  sends a reversing valve fault alert  140  for presentation on the thermostat  134 . For example, the fault alert  140  may indicate that the reversing valve  110  is in the cooling configuration of  FIG.  1 A  rather than the appropriate heating configuration of  FIG.  1 B  for the currently requested heating operating mode  138 . In some embodiments, the alert  140  may also or alternatively be provided to a third-party (e.g., an administrator or maintenance provider of the HVAC system  100 ). This may provide for more rapid correction of the fault or malfunction of the reversing valve  110 . At step  216 , the controller  142  may stop operation of the HVAC system  100 . Stopping operation of the HVAC system  100  may prevent damage to the system  100 . 
     Modifications, additions, or omissions may be made to method  200  depicted in  FIG.  2   . Method  200  may include more, fewer, or other steps. For example, steps may be performed in parallel or in any suitable order. While at times discussed as controller  142 , HVAC system  100 , or components thereof performing the steps, any suitable HVAC system  100  or components of the HVAC system  100  may perform one or more steps of the method  200 . 
     Example Detection of a Reversing Valve Stuck in an Equalizing Configuration 
       FIG.  3    is a flowchart of an example method  300  of operating the HVAC system  100  for detecting when reversing valve  110  is stuck in the equalizing configuration illustrated in  FIG.  1 C . For example, the method  300  may be used to detect that the reversing valve  110  is stuck in the equalizing configuration of  FIG.  1 C  when either the cooling configuration of  FIG.  1 A  or the heating configuration of  FIG.  1 B  is indicated by the current operating mode  138 . 
     Method  300  may begin at step  302  where the suction-side properties  144  are monitored. In this example, the suction-side properties  144  include a suction-side temperature  144   a  and a suction-side pressure  144   b . The controller  142  may receive the suction-side properties  144  from the sensor(s)  106  intermittently (e.g., several times per second, each second, or the like) and store measurements of the suction-side properties  144 . At step  304 , the liquid-side properties  146  are monitored. In this example, the liquid-side properties  146  include a liquid-side temperature  146   a  and a liquid-side pressure  146   b . The controller  142  may receive the liquid-side properties  146  from the sensor(s)  108  intermittently (e.g., several times per second, each second, or the like) and store measurements of the liquid-side properties  146 . 
     At step  306 , the controller  142  determines whether the suction-side temperature  144   a  is less than the liquid-side temperature  146   a . For example, the controller  142  may determine a difference between the suction-side temperature  144   a  and the liquid-side temperature  146   a . If this difference is less than zero, the controller  142  may determine that the suction-side temperature  144   a  is less than the liquid-side temperature  146   a . In some embodiments, the difference may be compared to a threshold value (e.g., a threshold of the thresholds  408  described with respect to  FIG.  4    below), and, in order for the suction-side temperature  144   a  to be considered less than the liquid-side temperature  146   a , the difference must be less than (e.g., more negative than) the threshold value. In some embodiments, the criteria of step  306  must be satisfied for at least a minimum time interval (e.g., of at least 30 seconds, e.g., of at least one minute, e.g., of at least five minutes) in order for the suction-side temperature  144   a  to be considered less than the liquid-side temperature  146   a . If, at step  306 , the suction-side temperature  144   a  is not less than the liquid-side temperature  146   a , the controller  142  proceeds to step  308 . Otherwise, if the heat suction-side temperature  144   a  is less than the liquid-side temperature  146   a , the controller  142  proceeds to step  312  (i.e., bypassing the other determinations associated with steps  308  and  310 ). In other words, the determination at step  306 , based on a comparison of the suction-side temperature  144   a  and liquid-side temperature  146   a , may be used as an initial test to determine whether the reversing valve  110  is stuck in the equalizing configuration of  FIG.  1 C . 
     At step  308 , the controller  142  determines whether a ratio of the liquid-side pressure  146   b  to the suction-side pressure  144   b  is less than a threshold value (e.g., a threshold of thresholds  408  described with respect to  FIG.  4    below). For example, the controller  142  may calculate a ratio of the liquid-side pressure  146   b  to the suction-side pressure  144   b  and compare the resulting ratio to a threshold value. In some embodiments, the criteria of step  308  must be satisfied for at least a minimum time interval (e.g., of at least 30 seconds, e.g., of at least one minute, e.g., of at least five minutes) in order for the ratio to be considered less than the threshold value. If the criteria of step  308  are not satisfied, the controller  142  returns to steps  302  and  304  to monitor the suction-side properties  144  and liquid-side properties  148 , respectively. However, if the criteria of step  308  is satisfied, the controller  142  proceeds to step  310 . 
     At step  310 , the controller  142  determines whether the suction-side temperature  144   a  of the suction-side properties  144  has an increasing trend. For example, the controller  142  may determine whether the value of the suction-side temperature  144   a  increases during a period of time, following the determination at step  308  that the ratio of the liquid-side pressure  146   b  to the suction-side pressure  144   b  is less than the predefined threshold value. In some embodiments, a trend in the suction-side temperature  144   a  is determined based on a rate of change of the suction-side temperature  144   a  (e.g., a time derivative of stored values and/or instantaneous values of the suction-side temperature  144   a ). For example, the controller  142  may determine a rate of change of the suction-side temperature  144   a  over a period of time. The controller  142  may determine if the rate of change is positive (i.e., greater than zero) for a predefined period of time (e.g., for 30 seconds or more). In some embodiments, if the rate of change has been positive for the period of time, the controller  142  may determine that the suction-side temperature  144   a  has an increasing trend at step  310 . In some embodiments, in order to determine that the suction-side temperature  144   a  has an increasing trend, the controller  142  may determine that the rate of change of the suction-side temperature  144   a  is both positive and greater than a threshold value for a minimum period of time. In some embodiments, the controller  142  may determine, for a period of time, a difference between an initial value (e.g., at the start of the period of time) of the suction-side temperature  144   a  and a final value (e.g., at the end of the period of time) of the suction-side temperature  144   a . If this difference is greater than a threshold value (e.g., a threshold of thresholds  408  described with respect to  FIG.  4    below), the controller  142  may determine that the of the suction-side temperature  144   a  has an increasing trend at step  310 . If the controller  142  determines the of the suction-side temperature  144   a  does not have an increasing trend, the controller  142  returns to steps  302  and  304  to monitor the suction-side properties  144  and liquid-side properties  146 , respectively. Otherwise, if the controller  142  determines that the suction-side temperature  144   a  has an increasing trend, the controller  142  proceeds to step  312 . 
     At step  312 , the controller  142  determines that a reversing valve fault is detected and that the reversing valve  110  is stuck in the equalizing configuration illustrated in  FIG.  1 C . In some embodiments, prior to determining that the reversing valve fault is detected, the controller  142  first confirms that the HVAC system  100  is operating (e.g., that there is either a current heating or cooling demand). In other words, the controller  142  may confirm that the HVAC system  100  as a prerequisite to determining that the reversing valve fault is detected. When the HVAC system  100  is not running (i.e., not providing heating or cooling), it may be appropriate and/or acceptable for the reversing valve  110  to be in the equalizing configuration of  FIG.  1 C . In some embodiments, the controller  142  may test whether the valve is responsive and can be moved out of the equalizing configuration (e.g., as described with respect to step  212  of  FIG.  2    above). At step  314 , the controller  142  sends a reversing valve fault alert  140  for presentation on the thermostat  134 . For example, the fault alert  140  may indicate that the reversing valve  110  is stuck in the equalizing configuration of  FIG.  1 C . In some embodiments, the fault alert  140  may also or alternatively be provided to a third-party (e.g., an administrator or maintenance provider of the HVAC system  100 ). This may facilitate the more rapid correction of the fault or malfunction of the reversing valve  110 . At step  316 , the controller  142  may automatically stop operation of the HVAC system  100 . For example, the controller  142  may cause the compressor  104  to stop operating (e.g., to shut off). The controller  142  may also cause one or both of the fan  114  and the blower  126  stop operating (e.g., shut off). Stopping operation of the HVAC system  100  may prevent damage to one or more components of the HVAC system  100  and reduce the expenditure of energy without providing desired conditioning to a space while the reversing valve  110  is stuck in the equalizing configuration of  FIG.  1 C . 
     Modifications, additions, or omissions may be made to method  300  depicted in  FIG.  3   . Method  300  may include more, fewer, or other steps. For example, steps may be performed in parallel or in any suitable order. While at times discussed as controller  142 , HVAC system  100 , or components thereof performing the steps, any suitable HVAC system  100  or components of the HVAC system  100  may perform one or more steps of the method  300 . 
     Example Controller 
       FIG.  4    is a schematic diagram of an embodiment of the controller  142 . The controller  142  includes a processor  402 , a memory  404 , and an input/output (I/O) interface  406 . 
     The processor  402  includes one or more processors operably coupled to the memory  404 . The processor  402  is any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g. a multi-core processor), field-programmable gate array (FPGAs), application specific integrated circuits (ASICs), or digital signal processors (DSPs) that communicatively couples to memory  404  and controls the operation of HVAC system  100 . The processor  402  may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor  402  is communicatively coupled to and in signal communication with the memory  404 . The one or more processors are configured to process data and may be implemented in hardware or software. For example, the processor  402  may be 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture. The processor  402  may include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory  404  and executes them by directing the coordinated operations of the ALU, registers, and other components. The processor may include other hardware and software that operates to process information, control the HVAC system  100 , and perform any of the functions described herein (e.g., with respect to  FIGS.  2  and  3   ). The processor  402  is not limited to a single processing device and may encompass multiple processing devices. Similarly, the controller  142  is not limited to a single controller but may encompass multiple controllers. 
     The memory  404  includes one or more disks, tape drives, or solid-state drives, and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory  404  may be volatile or non-volatile and may include ROM, RAM, ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM). The memory  404  is operable to measurements of the suction-side properties  144 , liquid-side properties  146 , heat exchanger temperature  148 , and outdoor temperature  150 , threshold values  408 , and any other logic or instructions associated with performing the functions described in this disclosure (e.g., described above with respect to methods  200  and  300  of  FIGS.  2  and  3   ). The threshold values  408  generally include any of the threshold values described above with respect to the example methods  200  and  300  of  FIGS.  2  and  3   . 
     The I/O interface  406  is configured to communicate data and signals with other devices. For example, the I/O interface  406  may be configured to communicate electrical signals with components of the HVAC system  100  including the compressor  104 , the suction-side sensor(s)  106 , the liquid-side sensor(s)  108 , the reversing valve  110 , the fan  114 , the heat exchanger sensor  118 , the expansion devices  120 ,  122 , the blower  126 , outdoor temperature sensor  132 , and the thermostat  134 . The I/O interface may receive, for example, compressor signals, signals associated with any one or more of the sensors  106 ,  108 ,  118 ,  132 , thermostat calls, temperature setpoints, environmental conditions, and an operating mode status for the HVAC system  100  and send electrical signals to the components of the HVAC system  100 . The I/O interface  406  may include ports or terminals for establishing signal communications between the controller  142  and other devices. The I/O interface  406  may be configured to enable wired and/or wireless communications. 
     While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. 
     In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein. 
     To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112(f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.