Patent Publication Number: US-10767882-B2

Title: Refrigerant pump down for an HVAC system

Description:
TECHNICAL FIELD 
     This disclosure generally relates to a heating, ventilation, and air conditioning (HVAC) system, and more specifically to refrigerant pump down for the HVAC system. 
     BACKGROUND 
     Certain HVAC systems currently use mildly flammable refrigerant. Mildly flammable refrigerant may leak, causing unsafe concentrations of gas to be dispersed within a living environment. The unsafe concentrations of gas within the living environment may be perilous for the elderly and the sick. 
     SUMMARY 
     According to an embodiment, an HVAC system includes an indoor unit having an indoor blower, an outdoor unit having a compressor and a condenser, an isolation valve coupled to the outdoor unit, and a sensor to detect a refrigerant leak. The HVAC system further includes one or more controllers operable to generate an alarm in response to the sensor detecting the refrigerant leak, operate the indoor blower in response to generating the alarm, close the isolation valve in response to generating the alarm, and operate the compressor to pump down the refrigerant to the condenser in response to generating the alarm. 
     According to another embodiment, a method includes detecting, by a sensor of an HVAC system, a leak of refrigerant and generating an alarm in response to the sensor detecting the refrigerant leak. The method also includes operating an indoor blower of an indoor unit of the HVAC system in response to generating the alarm and closing an isolation valve coupled to an outdoor unit of the HVAC system in response to generating the alarm. The method further includes operating a compressor of the outdoor unit to pump down the refrigerant to a condenser of the outdoor unit in response to generating the alarm. 
     According to yet another embodiment, one or more computer-readable storage media embody instructions that, when executed by a processor, cause the processor to perform operations including detecting, by a sensor of an HVAC system, a leak of refrigerant and generating an alarm in response to the sensor detecting the refrigerant leak. The operations also include operating an indoor blower of an indoor unit of the HVAC system in response to generating the alarm and closing an isolation valve coupled to an outdoor unit of the HVAC system in response to generating the alarm. The operations further include operating a compressor of the outdoor unit to pump down the refrigerant to a condenser of the outdoor unit in response to generating the alarm. 
     Technical advantages of this disclosure may include one or more of the following. Embodiments of this disclosure may improve the overall safety of HVAC systems. For example, refrigerant (e.g., mildly flammable refrigerant) may be pumped down to an outdoor unit in response to a detected refrigerant leak. The outdoor unit contains the refrigerant, which prevents the refrigerant from accumulating in an indoor living space. Once the refrigerant is safely evacuated, the heating cycle can continue as normal. Avoiding lockout of the heating mode improves the safety of the individuals occupying the indoor living space by providing heat and reduces the probability property damage due to frozen, broken pipes. Pumping down the refrigerant to the outdoor unit in response to a sensor alarm or other indication of system leakage quickly contains and preserves the remaining refrigerant in the outdoor unit. 
     Embodiments of this disclosure may allow for detection of a defective sensor or false alarm. For example, pumping down the refrigerant by the outdoor compressor allows for the verification of safe refrigerant containment via a suction line pressure sensor or a pressure switch. The verification of the safe containment of the refrigerant may indicate a false alarm and/or a defective gas sensor. A false alarm or defective sensor will not lock out gas or electric heating. 
     Embodiments of this disclosure may pump down the refrigerant to the outdoor unit at the conclusion of each cooling cycle or in response to one or more weather conditions. For example, the refrigerant may be pumped down when the refrigerant will not be needed for an indefinite period of time (e.g., at the conclusion of a cooling season, during a cold spell, and so on). Pumping down the refrigerant may stop a refrigerant leak from occurring during the cooling off cycle and may stop refrigerant leaks at points that may not be detectable by a sensor (e.g., an expansion valve or concealed line sets). 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To assist in understanding the present disclosure, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an example system for pumping down refrigerant in an HVAC system; 
         FIG. 2  illustrates an example method for pumping down refrigerant in an HVAC system in response to a sensor alarm; 
         FIG. 3  illustrates an example method for pumping down refrigerant in an HVAC system in response to the conclusion of a cooling cycle; 
         FIG. 4  illustrates an example method for pumping down refrigerant in an HVAC system in response to one or more weather conditions; and 
         FIG. 5  illustrates an example computer system that may be used by the systems and methods described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Traditional mildly flammable HVAC systems require a gas sensor as part of the indoor equipment to detect the presence of a gas leak. Upon the detection of the gas leak, one or more modes of operation (e.g., a cooling mode and a heating mode) may be locked out until the sensor has detected that the gas concentration has dropped to safe level. When in lockout mode, a controller issues a command to discontinue operation of the cooling and/or heating cycle. Operation of the cooling and/or heating cycle will not resume until the cooling and/or heating unit is manually reset. For gas or electrical heating, a heating mode lockout can be perilous for the elderly and the sick and may create a high probability of property damage due to frozen, busted pipes. Embodiments of this disclosure provide a mildly flammable HVAC system that responds to a refrigerant leak while continuing to provide electric heat and/or gas heat. 
       FIGS. 1 through 5  show example systems and methods for pumping down refrigerant in an HVAC system.  FIG. 1  shows an example system for pumping down refrigerant in an HVAC system.  FIG. 2  shows an example method for pumping down refrigerant in an HVAC system in response to a sensor alarm,  FIG. 3  shows an example method for pumping down refrigerant in an HVAC system in response to the conclusion of a cooling cycle, and  FIG. 4  shows an example method for pumping down refrigerant in an HVAC system in response to one or more weather conditions.  FIG. 5  shows an example computer system that may be used by the systems and methods described herein. 
       FIG. 1  illustrates an example system  100  for pumping down refrigerant in an HVAC system. System  100  of  FIG. 1  includes an indoor unit  110 , an outdoor unit  130 , a refrigerant line  140 , and an isolation valve  150 . Indoor unit  110  of system  100  includes an evaporator  112 , a heating component  114 , a blower  116 , a gas sensor  118 , an alarm  120 , and a controller  122 . Outdoor unit  130  includes a compressor  132 , a condenser  134 , one or more fans  136 , and a controller  138 . 
     System  100  is an HVAC system that pumps down refrigerant (e.g., mildly flammable refrigerant) to outdoor unit  120  in response to one or more conditions. Pumping down the refrigerant contains the refrigerant in outdoor unit  130 , which prevents the refrigerant from accumulating in the indoor environment. Pumping down the refrigerant may include operating (e.g., activating) blower  116  of indoor unit  110 , closing isolation valve  150  (e.g., a liquid solenoid valve), and/or operating compressor  132  of outdoor unit  130  to pump down the refrigerant to condenser  134  of outdoor unit  130 . The one or more conditions that trigger the pump down may include an activation of alarm  120 , a determination that a cooling cycle of system  100  has ended, and/or a weather condition (e.g., a cold spell). 
     Indoor unit  110  of system  100  is any HVAC unit that is located within a structure. For example, indoor unit  110  of system  100  may be located in a closet or in an attic or a basement of a residential dwelling. Heating component  114  of indoor unit  110  is any component that provides or assists in providing heat to an indoor environment (e.g., a residential dwelling). For example, heating component  114  may be a furnace or an air handling unit. Heating component  114  may include one or more blowers  116 . Alternatively, blowers  116  may be separate from heating component  114 . Gas sensor  118  is a sensor that detects gas within an environment. For example, gas sensor  118  may be a flammable gas sensor that detects gas resulting from a refrigerant leak in system  100 . Gas sensor  118  may detect that a gas concentration of an indoor environment equals or exceeds a predetermined threshold. For example, the predetermined threshold may be a lower flammability limit (LFL) of a particular refrigerant (e.g., A2L refrigerant) as determined by one or more regulations, and gas sensor  118  may detect that the gas concentration of the indoor environment is equal to or greater than the LFL. 
     Alarm  120  of indoor unit  110  is any device that is operable to activate in response to one or more conditions (e.g., a detected refrigerant leak). Alarm  120  may be coupled to gas sensor  118 . Alarm  120  may activate if gas sensor  118  detects a gas concentration at or above the predetermined threshold. Activation of alarm  120  may send one or more signals to controller  120  of indoor unit  110 , controller  138  of outdoor unit  130 , one or more other components of system  100 , and/or a component outside of system  100  (e.g., a local fire department). Alarm  120  may include a critical alarm that activates if a count of the alarm (i.e., the number of times the alarm has been activated) exceeds a predetermined limit. The alarm count may be reset after a predetermined time period (e.g., an hour or a day). Controller  122  of indoor unit  120  is a component that controls operation of one or more components of system  100 . For example, controller  122  may control operation of evaporator  112 , heating component  114 , blower  116 , gas sensor  118 , and/or alarm  120 . 
     Outdoor unit  130  of system  100  is any HVAC unit that is located outdoors. For example, outdoor unit  130  of system  100  may be located in a backyard of a residential dwelling containing indoor unit  110 . Compressor  132  of outdoor unit  130  is any component that is operable to pump down refrigerant to condenser  134 . Condenser  134  of outdoor unit is any component that is operable to receive and store the refrigerant pumped down from compressor  132 . Fan  136  of outdoor unit  130  is any component operable to blow air across condenser  134 . Fan  136  includes a fan motor. Outdoor unit  130  may include a suction line pressure sensor or a pressure switch to verify safe refrigerant containment in outdoor unit  130 . 
     Refrigerant line  140  of system  100  transfers liquid refrigerant unidirectionally from outdoor unit  130  to indoor unit  110 . The refrigerant may be a mildly flammable refrigerant (e.g., an A2L refrigerant), a refrigerant with a lower flammability (e.g., A2 refrigerant), or a refrigerant with a higher flammability (e.g., an A3 refrigerant). Isolation valve  150  is coupled (e.g., physically connected) to refrigerant line  140 . Isolation valve  150  is operable to prevent the refrigerant from flowing to indoor unit  110 . Isolation valve  150  may be a liquid solenoid valve or an electronic expansion valve. 
     Although this disclosure describes and depicts system  100  including particular components arranged in a particular order, this disclosure recognizes that system  100  may include (or exclude) one or more components and the components may be arranged in any suitable order. For example, outdoor unit  130  may include a weather sensor operable to detect an outside temperature. As another example, alarm  120  may be located externally to indoor unit  110 . As still another example, indoor unit  112  may be replaced with a packaged unit (e.g., an outdoor packaged unit) where evaporator  112  and blower  116  of the packaged unit are located outdoors but the ductwork associated with the packaged unit is connected to an indoor space. As another example, controllers  122  and  138  may be integrated into one component. Given the teachings herein, one skilled in the art will understand that system  100  may include additional components and devices that are not presently illustrated or discussed but are typically included in a system such as a power supply, a distributor, and so on. In one embodiment, system  100  is an HVAC system for residential use. 
     Although  FIG. 1  illustrates a particular number of indoor units  110 , outdoor units  130 , refrigerant lines  140 , isolation valves  150 , evaporators  112 , heating components  114 , blowers  116 , gas sensors  118 , alarms  120 , controllers  122 , compressors  132 , condensers  134 , fans  136 , and controllers  138 , this disclosure contemplates any suitable number of indoor units  110 , outdoor units  130 , refrigerant lines  140 , isolation valves  150 , evaporators  112 , heating components  114 , blowers  116 , gas sensors  118 , alarms  120 , controllers  122 , compressors  132 , condensers  134 , fans  136 , and controllers  138 . For example, system  100  may include multiple indoor units  110  and outdoor units  130 . As another example, indoor unit  110  may include multiple controllers (e.g., a controller for alarm  120  and a controller for heating component  114 ). As still another example, system  100  may include a liquid line and a vapor line isolation valve as needed to fully isolate and retain refrigerant. 
     In operation, gas sensor  118  of indoor unit  110  detects a refrigerant leak in an indoor environment by detecting a gas concentration above a certain threshold. Gas sensor  118  sends a signal to alarm  120  of indoor unit  110  to activate alarm  120 . Upon activation of alarm  120 , alarm  120  sends a signal to controller  122  to alert controller  122  of the refrigerant leak. In response to the activation of alarm  120 , controller  122  initiates operation of blower  116  of indoor unit  110  to ventilate the refrigerant leak. Controller  122  closes isolation valve  150  coupled to refrigerant line  140  in response to the activation of alarm  120  to contain the refrigerant in outdoor unit  130 , which prevents the refrigerant from accumulating in the indoor environment. Controller  122  initiates operation of compressor  132  of outdoor unit  130  in response to the activation of alarm  120  to pump down the refrigerant from compressor  132  to condenser  134  of outdoor unit  130 , where the refrigerant is safely stored until further instruction. 
     As such, system  100  of  FIG. 1  contains the refrigerant in outdoor unit  130  in response to a potential refrigerant leak without locking out the heating mode of the HVAC system. 
       FIG. 2  illustrates an example method  200  for pumping down refrigerant in response to activation of a sensor alarm in an HVAC system. Method  200  begins at step  202 . At step  204 , a controller (e.g., controller  122  and/or controller  138  of  FIG. 1 ) determines whether the sensor alarm of the HVAC system (e.g., system  100  of  FIG. 1 ) is active. The sensor alarm (e.g., alarm  120  of  FIG. 1 ) may activate in response to receiving a signal from a gas sensor (e.g., gas sensor  118  of  FIG. 1 ) indicating that a gas concentration in an indoor environment exceeds a certain threshold (e.g., an LFL value). The sensor alarm may send a signal to the controller indicating that the sensor alarm has been activated. If the controller determines that the sensor alarm is active, method  200  begins a pump down procedure outlined in steps  206  and  208 . At step  206 , the controller instructs an indoor blower (e.g., blower  116  of  FIG. 1 ) of the HVAC system to operate. Operation of the indoor blower ventilates the indoor environment. The controller may instruct the indoor blower to continue operation if the indoor blower is currently in operation. The controller may instruct the indoor blower to activate if the indoor blower is currently deactivated. 
     Method  200  advances from step  206  to step  208 , where the controller instructs an isolation valve (e.g., isolation valve  150  of  FIG. 1 ) to close. The isolation valve may be a liquid solenoid valve coupled to a refrigerant line (e.g., refrigerant line  140  of  FIG. 1 ) and/or an outdoor unit (e.g., outdoor unit  130  of  FIG. 1 ). Closing the isolation valve assists in containing the refrigerant in the outdoor unit, which may prevent the refrigerant from accumulating in the indoor environment. The controller also instructs a compressor (e.g., compressor  132  of  FIG. 1 ) of the outdoor unit to pump down the refrigerant to a condenser (e.g., condenser  134  of  FIG. 1 ) of the outdoor unit until one or more predetermined pump down rules are satisfied. Pump down can occur during any mode of operation (e.g., standby or off). An example pump down rule may include initiating the pump down if the gas sensor detects a level of refrigerant exceeding a predetermined limit. Another example pump down rule may include operating the compressor until a pressure switch or a sensor indicates that a refrigerant pressure of less than 20 pounds per square inch is achieved. For example, the compressor may continue operation until a suction pressure sensor reads 20 pounds per square inch gauge (psig) or less. Once 20 psig is reached, the compressor is turned off. If a pressure switch is used, a normally closed pressure switch with a set point of 20 psig may be used. Once the pressure reaches 20 psig, the pressure switch will open and turn the compressor off. Another example pump down rule may include terminating the pump down procedure if a time to reach the pressure switch or sensor trip point is excessive (e.g., greater than a predetermined amount of time). This delay may indicate that the isolation valve has failed to close properly. 
     Method  200  advances from step  208  to step  210 , where the controller determines whether the sensor alarm has been deactivated. If the sensor alarm is still active, method  200  continues through step  206  (continuing to operate the indoor blower) and step  208  (continuing to close the isolation valve and operate the compressor until one or more of the predetermined pump down rules are satisfied) until the sensor alarm has been deactivated. Once the controller determines at step  210  that the sensor alarm is no longer active, method  200  advances to step  212 , where the controller increments a count of the sensor alarm by one. For example, if the sensor alarm was previously activated four times within a predetermined time period, the controller increments the alarm count from a count of 4 to a count of 5. 
     Method  200  then advances to step  214 , where the controller compares the sensor alarm count to a predetermined sensor alarm count limit. The sensor alarm count limit may be any suitable integer. The sensor alarm count may be time dependent. For example, the sensor alarm count limit may reset after a predetermined amount of time (e.g., a minute, an hour, or a day). If the controller determines that the sensor alarm count is less than or equal to the predetermined sensor alarm count limit, method  200  advances to step  218 , which directs method  200  back to first step  202 . 
     If the controller determines that the sensor alarm count is greater than the predetermined sensor alarm count limit, method  200  advances to step  216 , where the controller locks out the cooling mode of the HVAC system, continues the isolation of refrigerant in the outdoor unit, and activates a critical alarm. Activation of the critical alarm may generate a visual or auditory message. For example, the critical alarm may produce a loud beeping noise to alert occupants of the indoor environment to evacuate. Activation of the critical alarm may send a visual or auditory message to one or more response teams. For example, the critical alarm may automatically generate a phone call or an email message to a local fire department alerting them of the gas concentration level. Method  200  advances from step  216  to step  218 , which directs method  200  back to first step  202 . 
     At step  204 , if the controller determines that the sensor alarm is not on, method  200  advances to step  220 , where the controller determines whether a cooling mode of the HVAC system is turned on. If the cooling mode is turned on, method  200  advances to step  222 , where the controller determines whether the cooling mode has been locked out. The cooling mode may be locked out in response to the detection of an unsafe condition or in response to exceeding the maximum allowable sensor alarm incidents. If the cooling mode has been locked out, method  200  advances to step  224 , which directs method  200  back to first step  202 . If the cooling mode has not been locked out, method  200  advances to step  226 , where the controller determines whether the compressor pumped down the refrigerant to the outdoor unit. 
     If the controller determines that the refrigerant has been pumped down to the outdoor unit, method  200  advances from step  226  to step  228 , where the controller instructs the HVAC system to open the isolation valve. Method  200  then advances to step  230 , where the controller instructs the HVAC system to function in normal operation. In normal operation, the compressor is in operation and the indoor blower is in operation. If the controller determines that the refrigerant has not been pumped down at step  226 , method  200  advances from step  226  to step  230  without opening the isolation valve. At step  230 , the controller instructs the HVAC system to function in normal operation. 
     Method  200  advances from step  230  to step  232 , where the controller determines whether the sensor alarm is active. If the sensor alarm is not active, method  200  moves back to step  230  and the HVAC system continues in normal operation. If the sensor alarm is active, method  200  moves from step  232  to step  234 , where the controller instructs the compressor to discontinue operation. Method  200  then advances from step  234  to step  206  to start the pump down procedure as described above. 
     If the controller determines at step  220  that the cooling mode has not been turned on, method  200  advances from step  220  to step  236 , where the controller determines whether a heating mode of the HVAC system is turned on. If the heating mode is not turned on, method  200  advances to step  238 , which directs method  200  back to first step  202 . If the heating mode is turned on, method  200  advances to step  240 , where the controller determines whether the cooling mode of the HVAC system has been locked out. If the cooling mode has been locked out, the controller instructs the HVAC system to initiate a back-up heat operation. If the cooling mode has not been locked out, the controller instructs the HVAC system to function in normal operation. 
     Method  200  advances from steps  242  and  243  to step  244 , where the controller determines whether the sensor alarm is active. If the sensor alarm is not active, method  200  moves back to step  240  to determine whether the cooling mode has been locked out. If the sensor alarm is active, method  200  moves from step  244  to step  246 , where the controller instructs the HVAC system to shut down the heating mode. Method  200  then advances to step  206  to start the pump down procedure as described above. 
     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  212 ,  214 , and  216  directed to incrementing the alarm count and activating the critical alarm may be eliminated. As another example, method  200  may include an additional step of verifying containment of the refrigerant in the outdoor unit using a suction line pressure sensor or a pressure switch. Steps may also be performed in parallel or in any suitable order. For example, step  220  directed to determining whether the HVAC system is in cooling mode may occur after step  236  directed to determining whether the HVAC system is in heating mode. As another example, step  208  of the pump down procedure may occur prior to step  206  of the pump down procedure. While discussed as specific components completing the steps of method  200 , any suitable component of the HVAC system may perform any step of method  200 . 
       FIG. 3  illustrates an example method  300  for pumping down refrigerant in response to the conclusion of an HVAC system&#39;s cooling cycle. Method  300  is similar to method  200  of  FIG. 2  with the exception of steps  326  through  338 , which illustrate the process of pumping down the refrigerant in response to the conclusion of the cooling cycle. Method  300  begins at step  302 . At step  304 , a controller (e.g., controller  122  of  FIG. 1 ) determines whether the sensor alarm of the HVAC system (e.g., system  100  of  FIG. 1 ) is on. If the sensor alarm is on, method  300  begins a pump down procedure as outlined in steps  306  and  308 . At step  306 , the controller instructs an indoor blower (e.g., blower  116  of  FIG. 1 ) of the HVAC system to operate. At step  308 , the controller instructs an isolation valve (e.g., isolation valve  150  of  FIG. 1 ) to close and a compressor (e.g., compressor  132  of  FIG. 1 ) of the outdoor unit to pump down the refrigerant to a condenser (e.g., condenser  134  of  FIG. 1 ) of the outdoor unit. 
     Method  300  advances from step  308  to step  310 , where the controller determines whether the sensor alarm has been deactivated. If the sensor alarm is still active, method  300  continues through step  306  (e.g., operating the indoor blower) and step  308  (i.e., closing the isolation valve and operating the compressor until one or more predetermined pump down rules are satisfied) until the sensor alarm has been deactivated. Once the controller determines at step  310  that the sensor alarm is no longer active, method  300  advances to step  312 , where the controller increments a count of the sensor alarm by one. Method  300  then advances to step  314 , where the controller compares the sensor alarm count to a predetermined sensor alarm count limit. If the controller determines that the sensor alarm count is less than or equal to the predetermined sensor alarm count limit, method  300  advances to step  318 , which directs method  300  back to first step  302 . If the controller determines that the sensor alarm count is greater than the predetermined sensor alarm count limit, method  300  advances to step  316 , where the controller locks out the cooling mode and activates a critical alarm. Method  300  then advances from step  316  to step  318 , which directs method  300  back to first step  302 . 
     At step  304 , if the controller determines that the sensor alarm is not on, method  300  advances to step  320 , where the controller determines whether a cooling mode of the HVAC system is turned on. If the cooling mode is on, method  300  advances to step  322 , where the controller determines whether the cooling mode has been locked out. If the cooling mode has been locked out, method  300  advances to step  324 , which directs method  300  back to first step  302 . If the cooling mode has not been locked out, method  300  advances to step  326 , where the controller instructs the HVAC system to open the isolation valve. Method  300  then advances to step  328 , where the controller instructs the HVAC system to function in normal operation (i.e., the compressor and the indoor blower are both in operation). 
     Method  300  advances from step  328  to step  330 , where the controller determines whether the sensor alarm is on. If the sensor alarm is on, method  300  moves from step  330  to step  332 , where the controller instructs the compressor to discontinue operation. Method  300  then advances from step  332  to step  306  to start the pump down procedure as described above. If the sensor alarm is not on, method  300  advances from step  330  to step  334 , where the controller determines whether the cooling mode of the HVAC system has been deactivated. 
     If the cooling mode of the HVAC system has not been deactivated at step  334 , method  300  moves to step  328 , where the controller instructs the HVAC system to continue normal operation. If the cooling mode of the HVAC system has been deactivated (i.e., the cooling cycle has concluded), method  300  advances to step  336 , where a pump down procedure is initiated. At step  336 , the controller instructs the compressor to continue operation, the isolation valve to close, and the compressor to pump down the refrigerant to the condenser until one or more predetermined pump down rules are satisfied. Method  300  then advances from step  336  to step  338 , which directs method  300  back to first step  302 . 
     If the controller determines at step  320  that the cooling mode has not been turned on, method  300  advances from step  320  to step  340 , where the controller determines whether a heating mode of the HVAC system is on. If the heating mode is not on, method  300  advances to step  342 , which directs method  300  back to first step  302 . If the heating mode is on, method  300  advances to step  344 , where the controller determines whether the cooling mode of the HVAC system has been locked out. If the cooling mode has been locked out, method  400  advances from step  344  to step  356 , where the controller instructs the HVAC system to initiate a back-up heat operation. If the cooling mode has not been locked out, method  400  advances from step  344  to step  347 , where the controller instructs the HVAC system to function in normal operation. 
     Method  300  advances from steps  346  and  347  to step  348 , where the controller determines whether the sensor alarm is on. If the sensor alarm is not on, method  300  advances to step  349 , where the controller determines whether the heat is off. If the heat is off, method  300  moves back to step  347  and the HVAC system continues in normal operation. If the heat is on, method  300  advances from step  349  to step  356 , where the pump down procedure is initiated. 
     If the sensor alarm is on at step  348 , method  300  advances from step  348  to step  350 , where the controller instructs the HVAC system to shut down the heating mode. Method  300  then advances from step  350  to step  306  to start the pump down procedure as described above. 
     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  312 ,  314 , and  316  directed to incrementing the alarm count and activating the critical alarm may be eliminated. Steps may also be performed in parallel or in any suitable order. For example, step  320  directed to determining whether the HVAC system is in cooling mode may occur after step  340  directed to determining whether the HVAC system is in heating mode. While discussed as specific components completing the steps of method  300 , any suitable component of the HVAC system may perform any step of method  300 . 
       FIG. 4  illustrates an example method  400  for pumping down a refrigerant in response to a weather condition. Method  400  is similar to method  200  of  FIG. 2  with the exception of steps  436  through  442 , which illustrate the process of pumping down the refrigerant in response to one or more weather conditions. Method  400  begins at step  402 . At step  404 , a controller (e.g., controller  122  of  FIG. 1 ) determines whether the sensor alarm of the HVAC system (e.g., system  100  of  FIG. 1 ) is on. If the sensor alarm is on, method  400  begins a pump down procedure as outlined in steps  406  and  408 . At step  406 , the controller instructs an indoor blower (e.g., blower  116  of  FIG. 1 ) of the HVAC system to operate. At step  408 , the controller instructs an isolation valve (e.g., isolation valve  150  of  FIG. 1 ) to close and a compressor (e.g., compressor  132  of  FIG. 1 ) of the outdoor unit to pump down the refrigerant to a condenser (e.g., condenser  134  of  FIG. 1 ) of the outdoor unit. 
     Method  400  advances from step  408  to step  410 , where the controller determines whether the sensor alarm has been deactivated. If the sensor alarm is still active, method  00  continues through step  406  (e.g., operating the indoor blower) and step  408  (i.e., closing the isolation valve and operating the compressor until one or more predetermined pump down rules are satisfied) until the sensor alarm has been deactivated. Once the controller determines at step  410  that the sensor alarm is no longer active, method  400  advances to step  412 , where the controller increments a count of the sensor alarm by one. Method  400  then advances to step  414 , where the controller compares the sensor alarm count to a predetermined sensor alarm count limit. If the controller determines that the sensor alarm count is less than or equal to the predetermined sensor alarm count limit, method  400  advances to step  418 , which directs method  400  back to first step  402 . If the controller determines that the sensor alarm count is greater than the predetermined sensor alarm count limit, method  400  advances to step  416 , where the controller locks out the cooling mode and activates a critical alarm. Method  400  then advances from step  416  to step  418 , which directs method  400  back to first step  402 . 
     At step  404 , if the controller determines that the sensor alarm is not on, method  400  advances to step  420 , where the controller determines whether a cooling mode of the HVAC system has been turned on. If the cooling mode is on, method  400  advances to step  422 , where the controller determines whether the cooling mode has been locked out. If the cooling mode has been locked out, method  400  advances to step  424 , which directs method  400  back to first step  402 . If the cooling mode has not been locked out, method  400  advances to step  426 , where the controller determines whether the refrigerant in the HVAC system has been pumped down to the condenser. If the refrigerant has been pumped down, method  400  advances from step  426  to step  428 , where the controller instructs the HVAC system to open the isolation valve. Method  400  then advances to step  430 , where the controller instructs the HVAC system to function in normal operation (i.e., the compressor and the indoor blower are both in operation). If the controller determines that the refrigerant has not been pumped down at step  426 , method  400  advances from step  426  to step  430  without opening the isolation valve. At step  430 , the controller instructs the HVAC system to function in normal operation. 
     Method  400  advances from step  430  to step  432 , where the controller determines whether the sensor alarm is on. If the sensor alarm is on, method  400  moves from step  432  to step  434 , where the controller instructs the compressor to discontinue operation. Method  400  then advances from step  434  to step  406  to start the pump down procedure as described above. If the sensor alarm is not on, method  400  advances from step  432  to step  436 , where the controller determines whether the cooling mode of the HVAC system has been deactivated. 
     If the cooling mode of the HVAC system has not been deactivated at step  436 , method  400  moves back to step  430 , where the controller instructs the HVAC system to continue normal operation. If the cooling mode of the HVAC system has been deactivated (i.e., the cooling cycle has concluded), method  400  advances to step  438 , where the controller determines whether one or more predetermined weather conditions are satisfied. The one or more predetermined weather conditions may include a temperature value, a humidity value, a precipitation value, an air pressure value, a wind direction value, a wind speed value, a predetermined date, a predetermined time, any combination of the aforementioned, and so on. The controller may receive the predetermined weather conditions from a database (e.g., a database stored in memory  504  of  FIG. 5 ). 
     The controller may determine that a weather condition is satisfied by comparing one or more weather conditions associated with the environment of the HVAC system to one or more predetermined weather conditions. The one or more weather conditions associated with the environment of the HVAC system may include a temperature value, a humidity value, a precipitation value, an air pressure value, a wind direction value, a wind speed value, an average temperature value over a predetermined time period (e.g., a predetermined number of days), a predicted outdoor temperature (e.g., a forecasted temperature for a specific date), combination of the aforementioned, and so on. For example, the weather condition associated with the environment of the HVAC system may be a current outdoor temperature and the predetermined weather condition may be a predetermined temperature of 60 degrees Fahrenheit, and the controller may determine that the predetermined weather condition is satisfied if the outdoor temperature of the environment is less than or equal to 60 degrees Fahrenheit. The controller may receive the weather conditions associated with the environment of the HVAC system from one or more sensors (e.g., a weather sensor attached to an outdoor unit of the HVAC system). 
     The controller may determine that a weather condition is satisfied by comparing one or more values associated with the HVAC system to one or more predetermined weather conditions. For example, the controller may determine that a weather condition is satisfied by comparing a current date to a predetermined date (e.g., the first day of winter). 
     If the controller determines that the one or more predetermined weather conditions are not satisfied, method  400  advances to step  442 , which directs method  400  back to first step  402 . If the controller determines that the one or more predetermined weather conditions are satisfied, method  400  advances to step  440  to initiate the pump down procedure. At step  440 , the controller instructs the compressor to continue operation, the isolation valve to close, and the compressor to pump down the refrigerant to the condenser until one or more predetermined pump down rules are satisfied. 
     If the controller determines at step  420  that the cooling mode has not been turned on, method  400  advances from step  420  to step  444 , where the controller determines whether a heating mode of the HVAC system is on. If the heating mode is not on, method  400  advances to step  446 , which directs method  400  back to first step  402 . If the heating mode is on, method  400  advances to step  448 , where the controller determines whether the cooling mode of the HVAC system has been locked out. Method  400  then advances to step  450 , where the controller instructs the HVAC system to function in normal operation. 
     Method  400  advances from step  450  to step  452 , where the controller determines whether the sensor alarm is on. If the sensor alarm is not on, method  400  moves back to step  450  and the HVAC system continues in normal operation. If the sensor alarm is on, method  400  advances from step  452  to step  454 , where the controller instructs the HVAC system to turn off the heat. Method  400  then advances from step  452  to step  406  to initiate the pump down procedure as described above. 
     Modifications, additions, or omissions may be made to method  400  depicted in  FIG. 4 . Method  400  may include more, fewer, or other steps. For example, steps  412 ,  414 , and  416  directed to incrementing the alarm count and activating the critical alarm may be eliminated. Steps may also be performed in parallel or in any suitable order. For example, step  420  directed to determining whether the HVAC system is in cooling mode may occur after step  444  directed to determining whether the HVAC system is in heating mode. While discussed as specific components completing the steps of method  400 , any suitable component of the HVAC system may perform any step of method  400 . 
       FIG. 5  shows an example computer system that may be used by the systems and methods described herein. For example, controllers  122  and  138  of  FIG. 1  may include one or more interface(s)  510 , processing circuitry  520 , memory(ies)  530 , and/or other suitable element(s). Interface  510  receives input, sends output, processes the input and/or output, and/or performs other suitable operation. Interface  510  may comprise hardware and/or software. 
     Processing circuitry  520  performs or manages the operations of the component. Processing circuitry  520  may include hardware and/or software. Examples of a processing circuitry include one or more computers, one or more microprocessors, one or more applications, etc. In certain embodiments, processing circuitry  520  executes logic (e.g., instructions) to perform actions (e.g., operations), such as generating output from input. The logic executed by processing circuitry  520  may be encoded in one or more tangible, non-transitory computer readable media (such as memory  530 ). For example, the logic may comprise a computer program, software, computer executable instructions, and/or instructions capable of being executed by a computer. In particular embodiments, the operations of the embodiments may be performed by one or more computer readable media storing, embodied with, and/or encoded with a computer program and/or having a stored and/or an encoded computer program. 
     Memory  530  (or memory unit) stores information. Memory  530  may comprise one or more non-transitory, tangible, computer-readable, and/or computer-executable storage media. Examples of memory  530  include computer memory (for example, RAM or ROM), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), database and/or network storage (for example, a server), and/or other computer-readable medium. 
     Herein, a computer-readable non-transitory storage medium or media may include one or more semiconductor-based or other integrated circuits (ICs) (such as field-programmable gate arrays (FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs), hybrid hard drives (HHDs), optical discs, optical disc drives (ODDs), magneto-optical discs, magneto-optical drives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes, solid-state drives (SSDs), RAM-drives, SECURE DIGITAL cards or drives, any other suitable computer-readable non-transitory storage media, or any suitable combination of two or more of these, where appropriate. A computer-readable non-transitory storage medium may be volatile, non-volatile, or a combination of volatile and non-volatile, where appropriate. 
     Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context. 
     The scope of this disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that a person having ordinary skill in the art would comprehend. The scope of this disclosure is not limited to the example embodiments described or illustrated herein. Moreover, although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, feature, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, features, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Additionally, although this disclosure describes or illustrates particular embodiments as providing particular advantages, particular embodiments may provide none, some, or all of these advantages.