HVAC Unit Identification Device and Method

Abstract

A device for pulsing the control lines of an HVAC system in order for a user to discover which outside unit is associated with a particular inside unit. Lead wires from the device connect to the control contacts on the thermostat of an HVAC unit. The device is an electrical or electromechanical circuit that can use the power contained within the thermostat or can be battery powered. Once the device is connected, it pulses the control line for the reversing valve, in the case of a heat pump system, or pulses the control line for the compressor, for a cooling-only system. This pulsing creates a loud clicking sound in either case that allows the repair technician to decipher the correct outside unit corresponding to the inside unit without use of a helper.

Claims

1. A method for determining in an installation having multiple HVAC systems, each of said systems including an inside HVAC unit, an outside HVAC unit, and a thermostat having a control wire controlling either a reversing valve or a compressor start contactor in said outside HVAC unit, which outside HVAC unit is connected to a selected inside HVAC unit, comprising: a. providing a pulse generator, said pulse generator producing a pulsed output signal; b. selecting a particular thermostat associated with a particular inside HVAC unit; c. connecting said pulse generator to said control wire of said selected thermostat so that said pulsed output signal is applied to said control wire; d. while said pulse generator remains attached to said control wire, listening for a noise produced by the cycling of said reversing valve or said compressor start contactor in said outside HVAC unit in order to determine which outside HVAC unit is connected to said selected thermostat.

2. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 1, wherein power for said electrical pulse generator is provided by a battery.

3. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 1, wherein power for said electrical pulse generator is provided by said selected thermostat.

4. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 3, wherein power for said electrical pulse generator is provided by connecting said electrical pulse generator to a 24 VAC line on said selected thermostat.

5. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 1, wherein said pulsed signal is created in said electrical pulse generator using an electromechanical relay.

6. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 1, wherein said pulsed signal is created in said electrical pulse generator using an integrated circuit including a timer function.

7. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 2, wherein said pulsed signal is created in said electrical pulse generator using an electromechanical relay.

8. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 2, wherein said pulsed signal is created in said electrical pulse generator using an integrated circuit including a timer function.

9. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 3, wherein said pulsed signal is created in said electrical pulse generator using an electromechanical relay.

10. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 3, wherein said pulsed signal is created in said electrical pulse generator using an integrated circuit including a timer function.

11. A method for determining which outside HVAC unit is associated with a selected inside HVAC unit in an installation having multiple outside units and multiple inside units, comprising: a. providing a plurality of split HVAC systems, wherein each HVAC system includes, i. an inside HVAC unit, ii. a thermostat connected to said inside HVAC unit, iii. an outside HVAC unit, connected to said thermostat by at least one control wire, said control wire controlling either a reversing valve or a compressor start contactor in said outside HVAC unit; b. providing an electrical pulse generator, said pulse generator producing a pulsed output signal; c. selecting a particular thermostat; d. connecting said electrical pulse generator to said control wire connecting said selected thermostat to said outside HVAC unit connected to said selected thermostat; e. activating said electrical pulse generator in order to place a pulsed signal on said control wire; and f. while said pulse generator remains attached to said control wire, listening for a noise produced by the cycling of said reversing valve or said compressor start contactor in said outside HVAC unit in order to determine which outside unit is connected to said selected thermostat.

12. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 11, wherein power for said electrical pulse generator is provided by a battery.

13. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 11, wherein power for said electrical pulse generator is provided by said selected thermostat.

14. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 13, wherein power for said electrical pulse generator is provided by connecting said electrical pulse generator to a 24 VAC line on said selected thermostat.

15. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 1, wherein said pulsed signal is created in said electrical pulse generator using an electromechanical relay.

16. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 11, wherein said pulsed signal is created in said electrical pulse generator using an integrated circuit including a timer function.

17. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 12, wherein said pulsed signal is created in said electrical pulse generator using an electromechanical relay.

18. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 12, wherein said pulsed signal is created in said electrical pulse generator using an integrated circuit including a timer function.

19. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 13, wherein said pulsed signal is created in said electrical pulse generator using an electromechanical relay.

20. A method for determining which outside HVAC unit is connected to a selected inside HVAC unit as recited in claim 13, wherein said pulsed signal is created in said electrical pulse generator using an integrated circuit including a timer function.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016] FIG. 1 is a plan view, showing a typical setup of a prior art split HVAC system.

[0017] FIG. 2 is a schematic view, showing a prior art split HVAC system using a heat pump cycle.

[0018] FIG. 3 is a schematic view, showing a prior art split HVAC system using a standard refrigeration cycle used for cooling-only.

[0019] FIG. 4 is a plan view, showing multiple apartments and the corresponding split HVAC systems.

[0020] 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).

[0021] 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).

[0022] FIG. 7 is a schematic view, showing the components of a prior art relay, such as may be used in the present invention

[0023] FIG. 8 is an elevation view, showing the front face of a thermostat typical of a split HVAC system.

[0024] FIG. 9 is a schematic view, showing the wiring and contacts located on the thermostat and control circuit of a cooling-only HVAC unit.

[0025] FIG. 10 is a schematic view, showing the wiring and contacts located on the thermostat and control circuit of a heat pump HVAC unit.

[0026] 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.

[0027]

TABLE-US-00001 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 current invention 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

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 an evaporator).

[0034] 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).

[0035] 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.

[0036] 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 of 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.

[0037] 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 valve 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 valve since there is not a reversing valve present. However, a large electromechanical start contactor is typically used to start the compressor.

[0038] 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.

[0039] 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.

[0040] The current invention 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 current invention 40 connect to the contacts for thermostat power 48 and reversing valve control 50 on thermostat 22. The pulsing device contained in current invention 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.

[0041] 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 inventive device 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).

[0042] FIG. 6 shows a sequential block diagram, illustrating the operation of another embodiment of the inventive device 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 a cooling-only HVAC system. In addition, this embodiment of current invention 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.

[0043] 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 invention 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 invention 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.

[0044] 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.

[0045] 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.

[0046] 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 pulsing portion of the invention.

[0047] 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 in energy costs.

[0048] 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 coming 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.

[0049] 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.

[0050] 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's start contactor.

[0051] 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.

[0052] Similarly, FIG. 10 shows the contacts on a thermostat 22 and control circuit 18; however, this represents contacts for a 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. A Iso, 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 W2, and reversing valve contact 88 is O.

[0053] 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 lines 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.

[0054] FIG. 1 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.

[0055] 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 above. Alligator clips 110 are attached to cooling control contact 74 (Y) and cooling power contact 71 (RC). Upon energizing the pulsing circuit in invention 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.