Patent Publication Number: US-9851112-B2

Title: HVAC unit identification device and method

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable 
     MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of heating, ventilation and air conditioning. More specifically, the invention comprises an electrical or electromechanical device that pulses the control line of an outdoor HVAC unit using the thermostat connections in order to indicate to a user which outdoor unit is associated with a particular indoor unit. 
     2. Description of Related Art 
     On most occasions heating, ventilation and air conditioning (HVAC) systems are set up with some components on the inside of a dwelling and some components on the outside. Such a system is often called a “split system.”  FIG. 1  shows an example of a prior art split system. Inside unit  12  is located inside dwelling  10  while outside unit  14  is located outside the dwelling. The user controls, along with some type of temperature sensing device, are most often located in thermostat  22 . Thermostat  22  has control lines  20  that run to control circuit  18  located within inside unit  12 . Additional control lines  20  run from control circuit  18  to outside unit  14 . In addition to control lines, refrigerant lines  16  run between inside unit  12  and outside unit  14 . These lines carry the working fluid that circulates within the HVAC system. 
     In the case of large apartment complexes, multiple outside HVAC units are often located behind the building or on the roof. The presence of multiple outdoor units can can make it difficult to determine which outside unit corresponds to a particular inside unit. This becomes an issue when air conditioning repair personnel need to access the outside unit, but are faced with a multitude of nearly identical units with no method for deducing which is the correct unit. This scenario is shown in  FIG. 4 . In the example of  FIG. 4 , there are multiple outside units  14  behind a group of apartments  24 . While  FIG. 4  shows only six apartments  24 , this situation becomes increasingly complex with the addition of more apartments (possibly occupying multiple floors). 
     Control and refrigerant lines run from the inside units  12  in each apartment  24  to an associated outside unit  14 . Due to the quantity of lines and the fact that portions of the lines may be concealed, it would be a complicated if not impossible task to follow the lines from the apartment to the correct outside unit. Therefore, another method is typically used. The current solution requires the repair technician to bring an additional helper along for the repair job. The helper is tasked with quickly switching the air conditioning unit on and off from the thermostat inside the apartment while the technician waits outside listening for which unit comes on. (The task of the technician and helper could easily be switched). In the case of an air conditioning unit with a heat pump, a typical method is to switch the unit from heating to cooling or vice-versa. This action actuates the reversing valve contained in the outside unit. The actuation of the reversing valve causes a loud click which may be easily head. 
     Those skilled in the art will know that the reversing valve in a heat pump outdoor unit directs the refrigerant to flow in a selected direction. In one direction the system is in cooling mode. In this mode the coils and fan inside the dwelling act as the evaporator and the outside coils act as the condenser, thus cooling the air inside the dwelling. When the valve is reversed to heating mode, the coils switch roles and the air inside the dwelling is heated. 
     Actuating the reversing valve, again located in the outside air conditioning unit, creates a distinct clicking sound which can be heard by a helper standing near the outside units. The helper may then identify which outdoor unit is associated with the thermostat that the other technician is manipulating. A cooling-only system does not have a reversing valve. In the case of a cooling-only unit, briefly switching the air conditioning unit on activates the start contactor for the compressor. This also generates a loud clicking sound. The outside helper is then able to correctly identify the outside unit by listening for this clicking sound. Developing a method to identity the correct outside unit without the need for a second technician on-site would reduce the cost of HVAC repair work in multi-unit situations. A device that does this automatically would allow only one technician to go out to a site, thus leaving the second technician available for another job and only paying one technician for a job that now only requires one person. It is also important that the device used to actuate the reversing valve be compatible with most air conditioning units. The proposed invention allows a single technician to identify the outside unit and is compatible with both heat pump and cooling-only systems. 
     BRIEF SUMMARY OF THE PRESENT INVENTION 
     The present invention comprises a simple electrical device that pulses a signal on a control line of an HVAC unit in order to allow the identification of an outside unit corresponding to a particular inside unit. The inventive device typically connects to the control lines at the thermostat. In the case of a heat pump system, the device pulses the control line connected to the reversing valve. This action briefly energizes the valve, thus switching it from heating to cooling mode, repeatedly. The device does not energize any other part of the system, it only switches the valve. The result of this pulsing of the reversing valve is a loud clicking noise. The repair technician leaves the device attached to the thermostat, and it continues to pulse. As the device pulses, this continuous clicking sound can be heard by the air conditioning repair technician when he or she walks outside to listen. The device hereby allows the technician to determine which outside unit is associated with the inside unit connected to the device inside the dwelling. 
     In the case of an HVAC system having only cooling capabilities, the inventive device pulses the control line of the start contactor for the compressor. This pulsing is quick enough so that the motor of the compressor is not engaged, but the start contactor does create a clicking sound, similar to the clicking heard from the reversing valve, when it is energized. The repair technician then listens outside for the clicking sound to determine the corresponding outside unit, as done with the heat pump unit. 
     The device connects to the existing wires contained in the thermostat of the air conditioning unit. This method allows the repair technician to connect the device to almost any air conditioning unit that he or she may encounter on the job. The device is preferably able to operate from the power contained in the thermostat or from power supplied by battery. 
     In addition to the previously stated attributes, the device comprises a circuit test function that tests for short circuits in the wires contained in the thermostat. The circuit has a breaker that trips with less current than the threshold of current of the breaker contained in the unit. By attaching the wires of the thermostat to wires of the circuit test (with the thermostat switched to off), the repair technician can determine whether there is a short in the circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a plan view, showing a typical setup of a prior art split HVAC system. 
         FIG. 2  is a schematic view, showing a prior art split HVAC system using a heat pump cycle. 
         FIG. 3  is a schematic view, showing a prior art split HVAC system using a standard refrigeration cycle used for cooling-only. 
         FIG. 4  is a plan view, showing multiple apartments and the correspond ins split HVAC systems. 
         FIG. 5  is a schematic view, showing a block diagram that indicates the operation and key elements needed for the current invention when connected to a heat pump system (battery-powered embodiment). 
         FIG. 6  is a schematic view, showing a block diagram that indicates the operation and key elements needed for the current invention when connected to a cooling-only system (thermostat-powered embodiment). 
         FIG. 7  is a schematic view, showing the components of a prior art relay, such as may be used in the present invention. 
         FIG. 8  is an elevation view, showing the front face of a thermostat typical of a split HVAC system. 
         FIG. 9  schematic view, showing the wiring and contacts located on the thermostat and control circuit of a cooling-only HVAC unit. 
         FIG. 10  is a schematic view, showing the wiring and contacts located on the thermostat and control circuit of a heat pump HVAC unit. 
         FIG. 11  is an elevation view, showing a thermostat with the front cover removed and an embodiment of the current invention connected to the thermostat contacts. 
       
         
           
             
                 
               
                 
                     
                 
                 
                   REFERENCE NUMERALS IN THE DRAWINGS 
                 
                 
                     
                 
               
              
                 
                     
                 
              
             
             
                 
                 
                 
                 
              
                 
                   10 
                   dwelling 
                   12 
                   inside unit 
                 
                 
                   14 
                   outside unit 
                   16 
                   refrigerant lines 
                 
                 
                   18 
                   control circuit 
                   20 
                   control lines 
                 
                 
                   22 
                   thermostat 
                   24 
                   apartment 
                 
                 
                   26 
                   compressor 
                   28 
                   reversing valve 
                 
                 
                   30 
                   outside coil 
                   32 
                   outside fan 
                 
                 
                   34 
                   expansion valve 
                   36 
                   inside coil 
                 
                 
                   38 
                   inside fan 
                   40 
                   pulse generator 
                 
                 
                   42 
                   battery 
                   44 
                   time-delayed relay 
                 
                 
                   48 
                   thermostat power 
                   50 
                   reversing valve control 
                 
                 
                   52 
                   solenoid 
                   54 
                   compressor control 
                 
                 
                   56 
                   start contactor 
                   58 
                   fan control 
                 
                 
                   60 
                   system control 
                   62 
                   connection wires 
                 
                 
                   64 
                   thermostat contacts 
                   66 
                   heating contact 
                 
                 
                   68 
                   common contact 
                   70 
                   24 VAC contact 
                 
                 
                   72 
                   fan contact 
                   74 
                   cooling contact 
                 
                 
                   76 
                   heating control line 
                   78 
                   common line 
                 
                 
                   80 
                   24 VAC line 
                   82 
                   fan line 
                 
                 
                   84 
                   cooling line 
                   86 
                   emergency heat contact 
                 
                 
                   88 
                   reversing valve contact 
                   90 
                   emergency heat line 
                 
                 
                   92 
                   reversing valve line 
                   94 
                   relay 
                 
                 
                   96 
                   relay coil 
                   97 
                   relay coil 
                 
                 
                   98 
                   relay coil contacts 
                   100 
                   spring 
                 
                 
                   102 
                   common contact 
                   104 
                   normally open contact 
                 
                 
                   106 
                   normally closed contact 
                   108 
                   armature 
                 
                 
                   110 
                   alligator clip 
                 
                 
                     
                 
              
             
           
         
       
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention uses an electrical or electromechanical device, such as a time delayed relay driven by a fixed voltage, to pulse the control lines of an HVAC unit. The pulse generating device may be referred to as a “pulse generator.”  FIG. 1  shows a schematic of a prior art split HVAC system in a dwelling  10 . This is a typical setup for an HVAC system found in a home or apartment. The split system has an inside unit  12  and an outside unit  14  that may sit behind or on top of the dwelling  10 . 
     The preferred embodiment of the present invention is attached to the thermostat  22 . It pulses the control lines  20 . These lines lead to control circuit  18  contained within inside unit  12 . Control lines  20  then run from inside dwelling  10  to outside unit  14 , activating the correct mechanism as described in the succeeding text. 
     For the case of a heat pump HVAC system, the inventive device pulses the control line for the reversing valve.  FIG. 2  shows a schematic of the refrigeration cycle of a heat pump that contains indoor unit  12  and outdoor unit  14 . This is a split system where refrigerant lines  16  run between the two units. As indicated by  FIG. 2 , the outdoor unit  14  contains compressor  26 , reversing valve  28 , outside coil  30  and outside fan  32 . There are refrigerant lines  16  running throughout the system, which transport refrigerant (in different states of matter) to the necessary components of the system. 
     This transportation is made possible by compressor  26 , the heart of the cycle. It pressurizes the refrigerant, pumping it into the outside or inside coil (depending on whether the system is in heating or cooling mode). The pressurized refrigerant leaves the compressor  26  through the refrigerant line  16  connecting the compressor to reversing valve  28 . As mentioned in the preceding text, reversing valve  28  allows one HVAC system to both heat and cool the dwelling rather than requiring two separate systems. Depending on what mode the system is in (heating or cooling), outside coil  30  receives refrigerant from reversing valve  28  or sends it. Outdoor fan  32  moves air over outside coil  30 . Indoor fan  38  moves air over indoor coil  36 . 
     Reversing valve  28  is commonly in an energized state during the cooling cycle (the energized state could just as easily be the heating cycle). In this state the pressurized refrigerant runs from compressor  26 , through reversing valve  28 , to outdoor coil  30  (which acts as a condenser), through expansion valve  34 , and then to indoor coil  36 . After passing through indoor coil  36  the gaseous refrigerant flows back through another portion of reversing valve  28  and then to the suction side of compressor  26 . 
     Reversing valve  28  is in a de-energized state during the heating cycle. In that state the pressurized refrigerant runs from compressor  26 , through the reversing valve to indoor coil  36 . The indoor coil operates as a condenser. The refrigerant then flows from indoor coil  36  through expansion valve  34  and then to outdoor coil  30  (which acts as a evaporator). 
     The indoor fan  38  forces air across the indoor coil  36 , which circulates the air through the dwelling to provide heating or cooling. The outdoor fan  32  forces ambient air over outdoor coil  30  to cool the outdoor coil (in air conditioning mode) or heat the outdoor coil (in heating mode). 
       FIG. 3  shows a schematic of a prior art split HVAC system that only cools. The system is similar to that seen in  FIG. 2 , except reversing valve  28  is absent and the refrigerant only circulates in one direction. The refrigerant line  16  coming from the inside coil  36  travels directly to the compressor  26 , and the refrigerant line  16  coming from the compressor  26  runs directly to the outside coil  30 . The system in  FIG. 3  does not allow for reversal. It can only work in cooling mode. The arrows on refrigerant lines  16  indicate the direction of refrigerant flow, where (as discussed in the preceding text) outside coil  30  always acts as the condenser and indoor coil  36  always acts as the evaporator. Units that only act as cooling systems may have electrical heating coils, a separate system for heating, such as a furnace or radiator, or may not need to be heated. 
     In a heat pump unit, when the reversing valve line is energized, the valve creates a clicking sound. This sound is generated by the solenoid used to actuate the reversing valve. A solenoid is an electromagnetic device used to adjust the position of the reversing valve when necessary. The clicking sound created is the sound of the activation the solenoid that adjusts the valve. Briefly and repeatedly pulsing the control line thus creates a continuous clicking sound that is audible to a person nearby.  FIG. 4  shows a prior art schematic of multiple apartments  24  with the corresponding outside A/C units  14  located behind the apartments  24 . When the current invention is connected to thermostat  22  inside a particular apartment  24 , the line leading to the reversing valve is quickly and repeatedly switched on and off. The technician leaves the invention inside and walks outside to listen for the clicking sound. This allows him to identify the outside unit corresponding to the particular apartment where the invention was connected to the thermostat. 
     In the case of an air conditioning unit that is not a heat pump, the unit can only cool. This type of HVAC system does not contain a reversing so the outside coil always acts as a condenser and the inside coil always acts as an evaporator, as discussed in the preceding text. This situation does not allow the current invention to pulse the line for the reversing since there is not a reversing valve present. However, a large electromechanical start contactor is typically used to start the compressor. 
     A start contactor is a large electromechanical device that acts as a converter in an HVAC system. A  24  VAC signal is sent from the thermostat to the start contactor. Once the start contactor is energized with the  24  VAC signal, the contacts are closed and a  240  VAC circuit is completed. The  240  VAC signal is used to power the compressor. This device allows the use of a relatively low  24  VAC control signal to govern a  240  VAC power signal Similar to the reversing valve, the start contactor also creates a clicking sound when the control line for the compressor is activated. By rapidly and periodically pulsing the cooling line on a straight cooling unit, the start contactor generates a continuous clicking sound, thereby realizing the same effect as that observed using the reversing valve in the heat pump system. The start contactor is only energized for a brief interval—too short a time to actually start the compressor spinning. 
     A sequential block diagram showing the operation of an embodiment of the inventive device is shown in  FIG. 5 . The diagram in  FIG. 5  may refer to a heat pump or an HVAC system that is cooling-only. In this embodiment, power is supplied to the pulsing circuit by a battery. However, the method of powering the invention has no bearing on the HVAC system for which it is being used and a variety of different power sources could be employed. 
     The pulse generator  40 , indicated in the block diagram, represents an embodiment that uses battery  42  to power time delayed relay  44  (or similar electrical circuit capable of creating a pulsed voltage). The electrical leads from the pulse generator  40  connect to the contacts for thermostat power  48  and reversing valve control  50  on thermostat  22 . The pulsing device contained in pulse generator  40  periodically connects power to reversing valve control  50  (It applies a voltage to the reversing valve control line). When connected, the  24  VAC signal travels to control circuit  18  located within inside unit  12 . That signal is then transmitted to solenoid  52  of reversing valve  28 , which is located in outside unit  14 . The rapid and periodic signal quickly energizes solenoid  52  and actuates reversing valve  28 . With this actuation, a clicking sound is heard from outside unit  14 , allowing the repair technician to locate the correct unit. 
     Another embodiment of the current invention allows for the device to be operated using power available on the thermostat itself rather than an external power source such as a battery. In this embodiment, the pulse generator has additional electrical lead wires connected to the pulsing circuit in order to provide power. The connection is preferably made using a temporary device such as such as alligator clips or the like (discussed further in the succeeding text). 
       FIG. 6  shows a sequential block diagram, illustrating the operation of another embodiment of the pulse generator when connected to a straight air conditioning unit. This figure shows the current embodiment connected to a cooling-only air conditioning system to exemplify the difference between how the device works with a heat pump system versus cooling-only HVAC system. In addition, this embodiment of pulse generator  40  is powered by thermostat power  48  ( 24  VAC) rather than an external battery. The thermostat power is connected to time delayed relay  44  (or similar electrical circuit capable of producing a pulsed output). While the invention is shown connected to a cooling-only air conditioning system, this is not to suggest that the externally-powered embodiment of the invention can only operate on a cooling-only system. This differentiation is simply to illustrate two separate embodiments of the invention (battery powered and thermostat powered). Either embodiment can be used on any type of HVAC system but in an attempt to reduce redundancy the battery powered device is shown connected to a heat pump system and the thermostat powered device is shown connected to a cooling-only system. The two devices could have easily been switched so that the thermostat powered invention was on the heat pump system and the battery powered device was on the cooling-only system. 
     Similar to the description in  FIG. 5 , the embodiment shown in  FIG. 6  quickly and periodically pulses the control lines contained in thermostat  22 . However, the electrical leads of pulse generator  40  connect to different thermostat contacts than those in  FIG. 5 . In the case of the straight air conditioning system, thermostat power  48  and compressor control  54  are the two contacts activated. As discussed previously, cooling-only units do not have a reversing valve. Consequently the invention must connect to the compressor control line. When the invention briefly and periodically connects the power to the compressor control line, the  24  VAC signal is sent to circuit control  18  located within inside unit  12 . Control circuit  18  directs the signal to outside unit  14 . The signal from pulse generator  40  energizes start contactor  56  for compressor  26 . Once start contactor  56  is energized, the plunger contained within the start contactor is pulled to complete the  240  VAC circuit to power compressor  26 . Start contactor  56  is only energized long enough to close the plunger, which creates the necessary clicking sound. It does not stay energized long enough to initiate rotation of the motor in the compressor  26 . Thus, the invention does not waste energy. 
       FIGS. 5 and 6  demonstrate the versatility of the current invention and the fact that it can be used on different types of HVAC systems. In addition, these figures demonstrate two methods for powering the device, either by battery or thermostat power. As those familiar with the art know, connecting an electrical circuit either to a battery or to the power line for the thermostat is a relatively simple task. The electrical or electromechanical circuit used to pulse the line described here is that of a time-delayed relay. However, this should not be taken as limiting the scope of the invention; it should be viewed as one possible embodiment used to describe a specific method for carrying out the current invention. 
     There are many, many different ways to create a circuit that generates a suitable pulsed voltage. One approach is to use a simple electromechanical relay.  FIG. 7  shows a prior art schematic of a relay switch  94 . The simplified illustration demonstrates a preferred embodiment of the current invention. Those familiar with the art will recognize that once a power source, such as power from the thermostat or a battery as described in the preceding text, is connected to coil contacts  98 , a magnetic field is generated. This magnetic field is created by the interaction of core  97  with coil  96  wrapped around the core. When coil  96  is not energized, spring  100  holds armature  108  in the position shown in  FIG. 7 . This position has armature  108  on the normally closed contact  106 . Once coil  98  is energized, the magnetic field produced attracts armature  108  downward with respect to the view shown in  FIG. 7 , thus connecting with the normally open contact  104 . In the case of the current invention, connecting to normally open contact  104  and common contact  102  would result in the circuit completing upon energizing the coil contacts using either a battery or the thermostat power. 
     The preceding text regarding  FIG. 7  demonstrates the simplicity of a relay switch. A relay switch is suggested in the text because it is a simple, readily-available and inexpensive component for the current invention. This is especially true in the case of a time-delayed relay, where the timing and switching components are contained in a single unit. The convenience and simplicity of a relay switch make a good fit for the current invention. Although it is a convenient option, a relay switch is not the only option for the pulsing portion of the invention. 
     As those familiar with the art will recall, a time-delayed relay can be set to cycle on and off. Connecting power to a relay switch, such as that found in  FIG. 7 , that has a timing component allows the device to quickly alternate between the normally open and normally closed contacts. In the case of the air conditioning system and current invention, the time-delay can be set so that the connection is only made for a very short amount of time. This enables only enough time to power the start contactor or reversing valve so the compressor motor or other components of the system do not power on. This is a significant component of the device, which will save the consumer to energy costs. 
     An example of a device that can control the timing aspect of the relay is a  555  timer. As those familiar with the art know, a  555  timer is an integrated circuit that comprises transistors, diodes and resistors. A  555  timer uses resistance and capacitance to bring a timing aspect to the circuit. The time constant of the RC circuit determines the pulse width coining from the timer. In order to adjust the timing and duration of the pulse, the resistance and capacitance of the resistors and capacitors in the system are changed. 
     A  555  timer has three modes, which include monostable, astable, and bistable. Monostable mode allows a single pulse to issue from the device, and bistable mode acts as a flip-flop circuit, which can be made to change states. The mode to be considered for the current purpose is the astable mode. This mode allows for continual pulsing, which is desired in this application. The frequency of the output (rectangular pulses) from the timer is determined by the resistance of the resistors and capacitance of the capacitor. Once these values are set, the device can pulse a relay switch (or many other devices) as desired in order to be used in the invention. 
       FIG. 8  shows the front face of a prior art thermostat. Thermostat  22  has fan control  58  and system control  60 . With  FIG. 8  in mind, the reader should consider  FIG. 9 . It shows a schematic of a typical wiring configuration for a thermostat that is a cooling-only air conditioning unit. There are five thermostat contacts  64  on thermostat  22 . From left to right, the contacts are heating  66 , common  68 ,  24  VAC (live)  70 , fan  72  and cooling  74 . As shown, the contacts are commonly represented by the letters (in the same order as above) W, C, R, G and Y, respectively. These letters represent the common labeling in a typical HVAC unit, and may or may not refer to the color of the wire. These contacts have a corresponding contact on the control circuit  18 , located in the inside unit. Heating control line  76 , common line  68 ,  24  VAC line  80 , fan control line  82  and cooling control line  84  run from the thermostat to said control circuit  18 . For use with such a cooling-only system, the present invention connects to cooling contact  74  (the Y contact), in order to send a signal to the compressor&#39;s start contactor. 
     The following serves to give the reader a better understanding of the relationship between the settings contained in thermostat  22  in  FIG. 8  and the wiring in  FIG. 9 . If the system control  60  and the fan control  58  in  FIG. 8  are set to “COOL” and “ON”, respectively, the wires in  FIG. 9  that are activated are  24  VAC  80 , fan  82  and cooling  74 . The cooling control line  84  runs to control circuit  18 , then to the outside unit. As was discussed in the preceding text, cooling control line  84  then activates the start contactor for the compressor to start the refrigeration cycle. The fan control line  72  activates the indoor fan, which forces air over the cooling coils in order to cool the dwelling. Another example of the relationship between the thermostat settings in  FIG. 8  and the wiring in  FIG. 9  is the configuration that the thermostat in  FIG. 8  is currently set to. The system control  60  is set to “OFF” while the fan control system  58  is set to “ON”. This disposition correlates to  24  VAC line  80  and fan control line  82  being activated. This corresponds to the fan running without any refrigeration cycle or cooling. 
     Similarly,  FIG. 10  shows the contacts on a thermostat  22  and control circuit  18 ; however, this represents contacts for heat pump air conditioning system. As  FIG. 10  indicates, there are more contacts for a heat pump system than a cooling-only system. An emergency heat contact  86  and reversing valve contact  88  are present on thermostat  22  as well as all the contacts found in  FIG. 9 . Also, some of the contact labels typical for a heat pump system are different. The different and added contact labels are as follows, emergency heat contact  86  is E, heating contact  66  is W 2 , and reversing valve contact  88  is O. 
     The important addition is reversing valve contact  88 , or the O contact. This is the contact the present invention connects to for a heat pump HVAC system. The reversing valve is energized when the system is in cooling mode. So when thermostat  22  in  FIG. 8  has fan control  58  set to “ON” (or “AUTO”) and system control  60  set to “COOL”, the control line, in  FIG. 10  activated are the reversing valve control line  92 , fan control line  82  and cooling control line  84 . The reversing valve is normally in heating mode when not energized (by default) so if the system control  60  in  FIG. 8  is switched to heat, the control lines activated are heating  76  and fan  82 . These configurations are well known to those familiar with the art. 
       FIG. 11  shows a diagram of thermostat  22  with the cover removed. This diagram is that of a thermostat for a cooling-only HVAC system. By comparing the contacts from  FIG. 9  to those in  FIG. 11 , the reader will observe that there is an extra contact in  FIG. 11 . The cooling  24  VAC power contact  71  is represented on thermostat  22  by RC. Usually, cooling power  71  is connected to  24  VAC contact  70 , or the R contact, by means of a jumper wire (for a cooling-only system). While this is not shown in  FIG. 9  for the sake of simplicity, it is necessary and helpful to show in  FIG. 11 . 
     There are numerous mechanisms that can be employed to attach the current invention to a thermostat.  FIG. 11  shows one such method. Thermostat  22  has the front cover removed exposing the contacts for the controls. A schematic of the front face of a prior art thermostat is shown in  FIG. 8 , and is discussed in the preceding text. Current invention  40  contains lead wires  62  attached to alligator clips  110 . Thermostat  22  shown in  FIG. 11  corresponds to an air conditioning unit that cools only, as stated hove. Alligator clips  110  are attached to cooling control contact  74  (Y) and cooling power contact  71  (RC). Upon energizing the pulsing circuit in pulse generator  40 , the circuit running through the A/C system is completed by means of alligator clips  110  and lead lines  62  connected to the cooling contact  74  and  24  VAC cooling contact  71 . Completion of said circuit results in energizing the start contactor, creating the clicking sound that is audible to someone near the outside unit. 
     In addition, a preferred embodiment of the invention comprises a method of testing for a short circuit within the thermostat. This circuit test function detects a short circuit in one of the thermostat control lines that run to the control circuit on the inside unit. It tests each line individually, which accounts for an air conditioning unit with a thermostat with any amount of control lines. 
     A typical unit has a breaker in the thermostat rated for 3-5 amps. Alternatively, the test function component of the current invention contains an internal breaker with a lower current rating. With the thermostat set to off, the device is attached to the thermostat contacts. Once the device is attached, the tripping of the breaker indicates that there is a short circuit. 
     The combination of a pulsing circuit for the application described previously and short circuit test operation is convenient for a repair technician. Both functions are implemented on the thermostat and connect electrically. Thus, it is convenient and cost-effective to use a device that is already connected to the thermostat to inspect the system for short circuits. 
     A specific description of the device has been established. Many other embodiments and applications are possible. For example, although heat-pump and AC-only systems have been discussed, the engine could also be applied to a heat-only refrigerant circulation system. The function, method of operation and preferred embodiment has been set forth, but the invention should be understood in the broad sense, as stated by the following claims rather than by any particular example given.