Patent Publication Number: US-6220043-B1

Title: Apparatus and method for control of a heat pump system

Description:
This application claims priority under 35 USC Section 119 (e) (1) of provisional application number 60/093,885 filed Jul. 23, 1998. 
    
    
     A microfiche appendix comprises 24 sheets of microfiche. 
     FIELD OF THE INVENTION 
     This application relates generally to heating, ventilating and air conditioning (HVAC) systems and more particularly to micro-controller based controls for heat pumps and electric furnaces. 
     A microfiche appendix is included totaling—microfiche and—frames 
     BACKGROUND OF THE INVENTION 
     The use of electronics in HVAC systems has become increasingly common in recent years and has grown to include heat pumps and electric furnaces. The use of electronics, with relays, to control electric heat, has only recently become practical through the use of zero, or near zero, voltage crossing switching techniques such as those disclosed and claimed in co-assigned U.S. Pat. No. 5,530,615, the contents of which is included herein by this reference. With respect to defrost controls, electronics have replaced electro-mechanical controls for a considerable period of time. 
     Conventional split systems for residential heat pumps have an indoor evaporator coil unit and an outdoor condenser coil unit with electronic controls for each unit receiving an input from a wall thermostat for either heating or cooling and for operating outputs such as electric resistive heat, fans, reversing valves and a compressor. Typically, some seven wires are required to interconnect the thermostat and the indoor control with six wires running out to the outdoor unit. It would be very desirable to reduce the wiring complexity from a standpoint of cost saving but also because many field failures occur due to miswiring during installation and decreasing the wiring connections would result in fewer failures. Even when the wiring is done correctly, however, there are undesirable functional limitations of the conventional control system. Ideally, the indoor fan should not be energized when the compressor is not operating, however, there are certain operational modes in which the indoor fan can be energized when the compressor is not energized such as in a lockout, either for a short or a long duration. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide apparatus and methods for controlling heat pumps and electric furnaces which overcome the above noted prior art limitations. Another object is the provision of such control apparatus and methods which result in improved efficiency of operation as well as an enhanced comfort performance. Yet another object of the invention is the provision of control apparatus and methods which result in fewer system components than conventional systems and with less complex wiring. 
     Briefly, in accordance with the invention, controls for the indoor and outdoor units are integrated into a single control with control of the evaporator (indoor) fan matched or synchronized with the compressor operation. The integrated control receives the defrost thermostat signal input from the outdoor unit and controls the reversing valve, condenser fan and compressor contactor by relays. This results in improved efficiency and comfort. For example, if the compressor has been shut off due to a pressure switch trip or anti-short cycle timer then the evaporator fan can be shut off during this period. This improves system efficiency because the heat convection transferal is maximized to a specific set point, a feature not available in conventional split system controls. In the heat mode, supplemental electric heat can also be energized. Additionally, the evaporator fan speed can be varied during defrost to improve comfort. Complete control of the electric heat, indoor fan, outdoor fan, reversing valve and compressor allows optimum control of the defrost operation in a manner not available in conventional systems. The electric heat can be initialized in anticipation of defrost, the outdoor fan can be enabled in anticipation of completion of defrost, and the reversing valve can be used to equalize system pressures at the end of each cycle. 
     Conventional heat pumps have been known to result in discomfort due to the limitations of the refrigerant. This problem is obviated by an integrated control made in accordance with the invention by synchronizing operation of the compressor and evaporator fan. For example, allowing the compressor to run allows the refrigerant to transfer heat to the heat exchanger. After the compressor has been running for a selected time, e.g., 30 seconds, the indoor fan is enabled thereby providing a warmer discharge air. 
     The control detects air flow problems due to improper installation, indoor (evaporator) fan failure and “stuck” on resistive heaters. If the thermal limit switch opens, the indoor blower fan is energized. If the switch opens for a continuous duration of a selected amount, e.g., 80 seconds, then the system is put into a hard lockout which maintains the indoor fan running and prevents the electric heat from being turned on. In addition, during any mode of operation, if the thermal limit switch opens and recloses four times, the system is put into a soft lockout which allows the evaporator fan to cycle with demand for heat/cool but prevents the electric heat from being turned on for a selected period, e.g., one hour. If, after one hour, the limit has not switched open, the counters are cleared and the heaters can be enabled. 
     The control is provided with on board diagnostics which can monitor all limit devices, pressure and thermal switches, and can provide a central location for troubleshooting. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified schematic block diagram showing a heat pump and electric heat furnace system having indoor and outdoor units and using an integrated control made in accordance with the invention; 
     FIG. 1 a  is a schematic block diagram showing an integrated control disposed in an outdoor unit; 
     FIGS. 2 a  and  2   b  together are a system connection diagram showing an integrated control, made in accordance with the invention, interconnected with a heat pump and an electric furnace; 
     FIGS. 3 a ,  3   b  and  3   c  together are a schematic wiring diagram of the FIGS. 1-2 b  integrated control; 
     FIG. 4 is a flow chart showing the main program of a system made in accordance with the invention; and 
     FIG. 5 is a flow chart showing the integration of the several components of the system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, a heat pump and electric furnace split system  10  comprises an electronic control  12  mounted in an indoor unit  2  with input signals to control  12  from room thermostat  6 , pressure sensor  24  and/or  26  and defrost sensor  22  disposed in an outdoor unit  4 . Outputs from control  12  are coupled to compressor contactor CC, condenser fan  16  and reversing valve  18  in the outdoor unit as well as components in the indoor system shown in FIG.  2 . More specifically, with respect to FIG. 2, an evaporator (indoor) fan  14 , condenser fan  16 , reversing valve  18 , wall thermostat connections R, C, W 1 , W 2 , G, O and Y, main contactor CC and a transformer  20  are shown along with defrost thermostat  22 , low pressure switch  24  and high pressure switch  26  interconnected with control  12 . Heater banks  1 ,  2  and  3 , each comprising first and second heating elements (Heaters  1 ,  1 A,  2 ,  2 A,  3 ,  3 A, respectively), are shown connected to pin connector P 1  along with a thermal limit switch  28 . Inputs to the control comprise R, 24 VAC, line frequency 50/60 Hz; C, 24 VAC common; Y, first stage (heat pump) heating; O, cooling; G, indoor or evaporator fan; W 1 , first stage supplemental heat; W 2 , second stage supplemental heat; DFST T&#39;STAT, liquid line sensor switch for defrost; LIM IN, thermal limit switch; PS 1  and PS 2 , high and low pressure switch cut-outs; 30, 60 and 90 MIN field selectable defrost inhibit timer pins with the default value when no shunt jumper is used being 90 minutes; TEST, defrost timer speed-up; TEST_IN, electric heat speed-up time; and L 1 , L 2 , high voltage 240 VAC. The outputs comprise CC, compressor contactor relay; reversing valve R or Y terminals; HTR 1 , heater bank  1 ; HTR 2 , heater bank  2 ; HTR 3 , heater bank  3 ; COND FAN, outdoor condenser fan; and FAN, indoor (evaporator) air handler fan. 
     Electronic controller  12 , shown in FIGS. 3A and 3B, comprise the following sections demarcated by dashed lines: Power Supply Circuit Section  12   a , Thermostat Input Section  12   b , Relay Power Output Section  12   c , Logic Voltage Output Section  12   d , Limit Input Section  12   e , Test Input Section  12   f , Defrost Sensor Input Section  12   g , 60 Hertz Clock Section  12   h , Oscillator Section  12   l , Shunt Select Input Section  12   j , Indoor Blower Fan Relay Output Section  12   k , Heater Driver Section  12   l , Relay Output Section  12   m  and Reset Circuit Section  12   n.    
     Power Supply Circuit Section  12   a    
     Power Supply Input Section  12   a  includes terminals QC 1 , QC 2  for connection to the secondary of transformer  20  which supplies 24 volts. Fuse F 1 , connected to the 24 volt AC input, protects the electronics and the transformer. The fused voltage is inputted into diodes D 1 -D 4 , D 7  and D 8  configured as a full wave rectifying circuit. The output of the rectifier feeds into Logic Voltage Output Section  12   d  and Relay Power Output Section  12   c.    
     Logic Voltage Output Section  12   d    
     Logic Voltage Output Section  12   d  is separated from the rectifying bridge by diode D 9 . Downstream from diode D 9  is a capacitor C 4  used to smooth out the rectified AC power. The resulting DC voltage is regulated down to 5 volts by current limiting resistor R 10  and a zener diode Z 5 . Capacitor C 3  and C 7  are used to filter out any voltage ripples that occur in the logic level supply. The circuit outputs 5 VDC across both capacitors C 3  and C 7 . 
     Relay Power Output Section  12   c    
     Relay Power Output Section  12   c  is separated from the rectifying bridge by diode D 23 . Capacitor C 2 , C 10 , C 11  and C 8  smooth the voltage from diode  23  providing an unregulated, rectified power source for several DC relays controlled by electronic control  12 , to be discussed. 
     Thermostat Input Section  12   b    
     The thermostat inputs receive a 24 VAC input when on and an earth ground signal when off. The inputs O, W 1 , W 2 , G, Y and PS all use a nearly identical circuit. Components R 29 , R 20 , R 8 , R 7 , R 1  and R 30  are pull down resistors that provide a reference to earth ground. Next in the circuit are zener diodes Z 9 , Z 4 , Z 3 , Z 2 , Z 1  and Z 12 , respectively. The zener diodes are used to set a voltage threshold for the input signals and assure that the inputs have reached a certain minimum voltage level before they can be read at the micro-controller. Resistors R 34 , R 6 , R 5 , R 4 , R 3  and R 44 , respectively, are used to load down the zener diodes. Resistors R 31 , R 17 , R 16 , R 15 , R 14  and R 45 , respectively, are tied to input pins  6  (PA 4 ),  3  (PA 7 ),  4  (PA 6 ),  5  (PA 5 ),  7  (PA 3 ) and  8  (PA 2 ), respectively of micro-controller Ul. These resistors serve to limit the current that can be inputted into micro-controller Ul and protect the micro-controller&#39;s inputs from electrical stress. 
     Defrost Sensor Input Section  12   g    
     Resistor R 28 , connected between terminal QC 16  and earth ground, is used to reference the signal to earth ground while resistors R 9  and R 46  current limit the input (pin  11 , PB 5 ) and protect micro-controller U 1  from electrical stress. The defrost sensor, thermostat  22  is closed during defrost cycles and loaded at 50 mA through fan relay K 3 , to be discussed below. 
     60 Hertz-Clock Section  12   h    
     Clock Section  12   h  connected to micro-controller U 1  at {overscore (IRQ)} (pin  2  of micro-controller U 1 ) is used to link earth ground to the logic ground of the micro-controller. The earth ground input provides a 60 Hertz signal that is used as a clock input. Resistors R 25  and R 24  provide current protection and a voltage reference for the micro-controller input. Zener diode Z 8  limits the voltage and capacitor C 6  aids in filtering electrical noise into controller U 1 . 
     Oscillator Section  12   i    
     Resistor R 43  and resonator OSC 1 , connected between OSC 1  and OSC 2  micro-controller inputs (pins  27 ,  26 ), provide the internal clock for the controller. 
     Limit Input Section  12   e    
     The state of the thermal limit  28  is monitored by micro-controller U 1 . Thermal limit  28  is used to break power to the relays being used to control auxiliary heat, i.e., heater banks  1 ,  2  and  3 , as well as to provide an input at pin  9  (PA 1 ) to the micro-controller which indicates the temperature conditions in the air handler of the system. The state (on/off) is inputted to the micro-controller via resistor R 19 . Resistor R 18  and zener diode Z 6  are used to reference the input to logic ground and to limit its potential to 5 volts (logic voltage). 
     Test Input Section  12   f    
     The test input, pin  10  (PAO) of micro-controller  12 , is used in the manufacture of the controller and by the user. The status of this input is used by the controller to access special operation timings needed to run final assembly tests. The circuit comprises resistor R 12  used to current limit the input to the controller and R 13  used to reference the signal to logic ground. 
     Indoor Blower Relay Section  12 K 
     Indoor blower fan  14  is controlled through relay K 1  which is a normally open relay activated by micro-controller U 1  via output pin  21  (PC 1 ) and pins  1 ,  16  of relay driver U 2 . The internal suppression diode (not shown) and zener Z 7  are used to suppress the electro-magnetic field when the relay is released. 
     Heater Driver Section  12   l    
     Electronic control  12 , as shown, can accommodate up to six external relays. These are connected and controlled by micro-controller U 1  via output pins  19 ,  18 ,  17  (PC 3 , PC 4 , PC 5 , respectively) and pins  3 ,  14 ;  4 ,  13  and  5 ,  12 , respectively of relay driver U 2  wired to connector P 1 . Two relays per output may be used. 
     Relay Output Section  12   m    
     Condenser fan  16 , the outdoor fan, is controlled by relay K 3  which is normally closed and which maintains the fan energized or running in the deactivated state. When the relay is activated through micro-controller output pin  16  (PC 6 ) and pin  6 ,  11  of relay driver U 2 , the condenser fan will be turned off. This is used during the defrost operation. Diodes D 12 , D 13  and D 15  are used to provide full wave rectified power to the relay coil (along with diode D 7  of Power Supply Circuit  12   a ). Diode D 26  is used to prevent back EMF from the relay into driver U 2 . The diodes are used since the power source for the relays is derived from the defrost thermostat, referenced supra. This provides a hardware interlock between the defrost sensor and the state of the condenser fan. If the defrost thermostat is not closed, the control cannot activate the condenser fan relay. Additionally, the circuit provides the advantage of placing electrical loading on the defrost thermostat contacts. 
     The system contactor CC is controlled by relay K 4  through micro-controller output pin  15  (PC 7 ) and pins  7 ,  10  of relay driver U 2 . The function of this relay is to inhibit operation of the compressor which is required between run cycles and during fault conditions. The operation of the relay is controlled by micro-controller U 1 , as noted, as well as the diode interlock provided by diodes D 16 , D 17  and D 19 . Diode D 25  is used to prevent back EMF from the relay into driver U 2 . If the Y 1 /PS signal, i.e., the pressure switch and Y signal combined, is not present (see QC 20  of Thermostat Input Section  12   b ), the relay cannot be operated thereby providing a hardware interlock. An additional benefit is derived from this circuit, like that of relay K 4  circuit, by adding loading to the Y 1 /PS input, i.e., the pressure switch contacts by means of the coil of relay  4  in parallel with capacitance C 13 . 
     Reversing valve  16  is controlled by normally open relay K 2  through micro-controller output pin  22  (PCO) which is connected through current limiting resistor R 41  to the base of transistor Q 2 . Diode  24  connected across the relay coil is used to suppress the electromagnetic field when the relay is released. Energization of relay K 2  causes valve  16  to operate. 
     Reset Circuit Section  12   n    
     Micro-controller U 1  requires a special circuit connected to micro-controller pin  1  {overscore ((RESET))} to handle the reset function during power up and power down cycles. This is accomplished by separating power from the relay power circuit through diode D 22 . Zener diode Z 11  is used to set a minimum voltage threshold prior to activating the circuit. Resistor R 39  is used to current limit the charging of capacitor C 9 . This acts to slow down the voltage rise during power up. Resistor R 40  is used to pull down the circuit to logic ground during a power drop out. Diode D 11  is used to clip the maximum voltage for the circuit to one voltage drop (0.7 volts) above logic voltage. 
     The control responds to thermostat inputs by turning the indoor fan on and delaying it off with the delay off being a timed function dependent upon the particular mode of operation. The control drives the off board heater relays which respond to the first and second supplemental heat requests. The heater elements are sequenced on based on the W 1  and W 2  inputs and in accordance with preselected timing. 
     Opening of the thermal limit which responds to over-temperature conditions in the air duct, results in the indoor fan instantly turning on. If the thermal limit opens and there still is a call for supplemental heat, the heaters will be disabled for a minimum preselected time of 10 seconds and then stage back on according to a predetermined sequence. The thermal limit must be closed for the heater relays to be re-enabled. A one hour soft lock-out occurs whenever the thermal limit opens a preselected number of times, e.g., four times. During the soft lock-out, the control disables all requests for heat. The four thermal limit counters can be cleared by either a power cycle of R and C or an on/off transition of W 1 , W 2  or Y. A hard lock-out results in the indoor blower fan being locked on and the disabling of the heaters and can happen if, in the soft lock-out, the thermal limit trips open or if the limit remains open for a continuous duration of a preselected time of 80 seconds. 
     The TEST_IN input results in a one-time speed up mode. This is for factory installed heat or rapid cycling. 
     With respect to the heat pump and defrost controls, when PS 1  and PS 2  are closed and there is a request for Y, the contactor CC is enabled after a preselected five minute anti-short cycle timer which begins whenever Y transitions from an on/off condition. If either PS 1  or PS 2  opens, the control will disable CC and begin an anti-short cycle period. The defrost times are based on a cyclic timer which accrue only when pressure switches and Y are present and the anti-short cycle delay has expired. A request for O (cooling) enables the reversing valve. 
     Once the inhibit times have expired and there is a request for Y, then the defrost function is enabled and the condenser fan is disabled, the Y request on enables HTR 1 , HTR 2  and HTR 3  and the reversing valve is enabled. If the PS 1  or PS 2  switch opens during defrost and Y is present then the electric heat is disabled. The heat pump operates in the defrost mode only if the control is in the heating phase and the liquid line thermostat is closed. If the liquid line thermostat opens, the defrost functions are bypassed. Defrosting continues until either 10 minutes have expired or the liquid line thermostat (thermal cut-out) opens. Termination of defrost clears all timers and restarts the inhibit period. The following sequence occurs, the supplemental heat is turned off, the condenser fan is enabled and the reversing valve is de-energized after a selected time delay (e.g., 8 seconds). 
     If the TEST selection is shunted the control will clear all thermal lock-outs and if Y is on will allow a speed-up mode of the heat pump&#39;s defrost cycle for a selected number of cycles (e.g., 8 cycles). 
     With reference to FIG. 4, the main program starts at  100  and at step  102  timing registers and inputs/outputs are initialized. At the next step,  104  the inputs/outputs are updated and the ROM is checked. At decision step  106 , if the control is in the manufacturing mode the program returns to step  104 , if not, it moves to decision step  108  which looks at whether an O (cooling) input is present. If not, the program goes to decision step  112 , to be discussed. If the O input is present the program goes to process step  110  which enables the reversing valve and then moves on to decision block  112  which looks to see if the five minute anti-short cycle compressor delay has expired. If the delay has not expired the program reverts back to step  108  but if the delay has expired the program goes to decision block  114  which looks to see if the Y (compressor) input is present. If not, the program goes to process step  118  to be discussed but if it is present the program goes to process step  116 , compressor contactor functions and step  118 , heater control functions and then on to step  120  controlling the indoor fan control. The program ends at  122  and cycles back to step  104 . 
     With reference to FIG. 5 which shows the flow diagram for the integration of the system&#39;s components, the program starts at  130  and at decision block  132  looks to see if there is a Y input signal. If not, the program cycles back to the start but if the Y signal is present the program moves on to decision block  134  which looks to see if there is an O input. If there is no cooling signal the program jumps to decision block  144 , to be discussed. If there is an O input the next step at  136  is to instantly turn on the evaporator fan. The program then goes on to decision block  138  and checks to see if the pressure switches are closed and if not the program cycles back to decision block  132 . If the pressure switches are closed then the compressor and the indoor fan are enabled at process step  140 . The cooling cycle then ends at  142  and the program cycles back to decision block  132 . 
     When the decision block  134  finds that there is no O input, the program jumps to decision block  144 , as mentioned above, which determines whether the control is in the defrost mode. If the answer is negative the program jumps ahead to process step  154  in which the evaporator fan 30 second delay on is initiated. If the answer in process step is positive the program goes to process steps  146 ,  148  providing selected optional features, i.e., enable a two-speed evaporator fan, if desired, of step  146  and/or enabling anticipatory electric heat of process step  148 . The evaporator fan is enabled in process step  150  with the program going on to decision step  152  to check on the status of the pressure switches. If the pressure switches are closed the program goes to step  156  providing an optional process step of enabling a two speed compressor. The program then goes to  158  which cycles back to start at  130 . If the pressure switches are not closed the program skips block  156 . 
     The decision steps  138  and  152  looking at the status of the pressure switches as a precursor of enabling the compressor results in the feature of being able to run the indoor or evaporator fan in synchronization with the compressor and is not available in conventional controls. The decision block  144  in which the status of defrost is checked allows the control to distinguish between a defrost cycle and an auxiliary heat cycle (signals W 1 , W 2 ). This feature is also not available in conventional controls. In accordance with the invention, the defrost cycle can be handled differently than in prior art controls with regard to electric heat staging, changing fan speeds or compressor speeds (steps  146 ,  148 ,  150 ) to optimize the defrost cycle for efficiency and comfort reasons. 
     Efficiency ratings serve as design parameters of heat pumps. The ratings can be maximized by having complete control of the total system by merging the electric heat/fan control board and the defrost control as described above. The control of the evaporator (indoor) fan, is, as a result, matched to the compressor operation. Because of the integration, the fan can be inhibited when the compressor is not running due to pressure switch trips or anti-short cycle periods. This improves system efficiency because the heat convection transfer is maximized to a specific set point. Conventional split system controls do not have this capability. Furthermore, conventional heat pumps have been known to result in discomfort due to the limitations of the refrigerant. This problem is obviated by controlling the compressor together with the evaporator fan. As mentioned above, by allowing the compressor to run, the refrigerant is allowed to transfer heat to the heat exchanger. The heat exchanger will blow air for a selected period of time, e.g., 30 seconds, after the compressor has been running. Once this time delay expires, the indoor fan is enabled providing a warmer discharge air. 
     Complete control of the electric heat, indoor fan, outdoor fan, reversing valve and compressor allows optimum defrost operation. The electric heat can be initialized in anticipation of defrost, the outdoor fan can be enabled in anticipation of completion and the reversing valve can be used to equalize system pressures at the end of each cycle. 
     The control of the present invention allows the control to detect air flow problems due to improper installation, indoor fan failure and stuck-on resistive heaters. If this switch opens, the indoor blower fan is energized. If this switch opens for a continuous duration of 80 seconds, then the system is put into a hard lock-out in which the indoor fan remains on and inhibits the electric heat from turning on. In addition, during any mode of operation, if the thermal limit opens and recloses four times, the system is put into soft lock-out in which the evaporator fan still cycles with the demand for heat/cool, but the electric heat is inhibited for one hour. If, after one hour, the limit has not switched open, the counters will be cleared and the heaters can be enabled. 
     
       
         
           
               
            
               
                   
               
               
                 Table A comprises a list of components used in a control 12 made in 
               
               
                 accordance with the invention. 
               
            
           
           
               
               
            
               
                 QTY 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 001 
                 CEM-1 PCB Board 
                 Board 
               
               
                 019 
                 ¼ QUICK CONNECTS 
                 QC2 QC3 QC4 QC5 QC6 QC7 QC8 QC9 
               
               
                   
                   
                 QC10 QC11 QC12 QC13 QC14 QC15 QC16 
               
               
                   
                   
                 QC17 QC18 QC19 QC20 
               
               
                 001 
                 {fraction (3/16)} QUICK CONNECTS 20 MIL 
                 QC1 
               
               
                 001 
                 12 PIN MATE &amp; LOK 
                 P1 
               
               
                 001 
                 5 AMP FUSE 
                 F1 
               
               
                 002 
                 VERT FUSE TERMINAL 
                 FT1 FT2 
               
               
                 001 
                 MPSA06 OR EQUIV (TAPE AND 
                 Q2 
               
               
                 002 
                 RES, 1K, ¼ W, 1% 
                 R32 R39 
               
               
                 004 
                 RES, 10K, ¼ W, 1% 
                 R19 R21 R27 R42 
               
               
                 013 
                 .022 JUMPER, NON-INSULATE 
                 J1 J2 J3 J4 J5 J6 J7 J8 J9 J10 J11 J12 J13 
               
               
                 023 
                 1N4007 DIODE 
                 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D12 D13 
               
               
                   
                   
                 D15 D16 D17 D19 D20 D21 D22 D23 D24 D25 
               
               
                   
                   
                 D26 
               
               
                 001 
                 HASCO SSD110PHDC24-14 
                 K3 
               
               
                 003 
                 ZENER, 1N5231, 5% .5 w 
                 Z5 Z6 Z8 
               
               
                 006 
                 ZENER, 1N5242, 5% .5 w 
                 Z1 Z2 Z3 Z4 Z9 Z12 
               
               
                 001 
                 ZENER, 1N5247, 5% .5 w 
                 Z11 
               
               
                 001 
                 ZENER, 1N5260, 5% .5 w 
                 Z7 
               
               
                 001 
                 MOTOROLA MC68HC705P9 
                 U1 
               
               
                 001 
                 ULN 2003A RELAY DRIVER 
                 U2 
               
               
                 002 
                 18 V P&amp;B SPDT T7C RELAY 
                 K2 K4 
               
               
                 007 
                 RES, 10K, ⅛ W, 5% 
                 R3 R4 R24 R25 R34 R40 R44 
               
               
                 010 
                 RES, 100K, ⅛ W, 5% 
                 R9 R12 R14 R15 R16 R17 R31 R37 R38 R45 
               
               
                 001 
                 RES, 1M, ⅛ W, 5% 
                 R43 
               
               
                 004 
                 RES, 2K, ⅛ W, 5% 
                 R11 R35 R36 R41 
               
               
                 005 
                 RES 51K, ⅛ W, 5% 
                 R5 R6 R13 R18 R46 
               
               
                 001 
                 CRYSTAL OSC, 2.0 MHZ. 
                 OSC1 
               
               
                 001 
                 CERM CAP Z5U .01 Uf, 50 V 
                 C6 
               
               
                 006 
                 RES, 1.5K, 2 W, 5% 
                 R1 R8 R10 R20 R28 R29 
               
               
                 002 
                 RES, 2K, 2 W, 5% 
                 R7 R30 
               
               
                 001 
                 .025 DUAL ROW HEADER (6 P 
                 P2 
               
               
                 004 
                 STANDOFFS (PLASTIC) 
                 S1 S2 S3 S4 
               
               
                 003 
                 POST STANDOFF (PLASTIC SU 
                 S5 S6 S7 
               
               
                 002 
                 10 uF, 16 V ELECTL RAD CAPS 
                 C3 C9 
               
               
                 002 
                 10 uF, 50 V ELECTL RAD CAPS 
                 C13 C14 
               
               
                 002 
                 47 uF, 50 V ELECTL RAD CAPS 
                 C4 C11 
               
               
                 001 
                 100 uF, 50 V ELECTL RAD CAP 
                 C10 
               
               
                 001 
                 DIODE 1N458A (TAPE AND RE 
                 D11 
               
               
                 001 
                 MOV FOR 24 VAC APPS (SIEME 
                 MOV1 
               
               
                 005 
                 .1 uF, 100 V FILM CAP, 20% 
                 C1 C2 C5 C7 C8 
               
               
                 001 
                 .47 uF, 63 VDC FILM CAP 
                 C12 
               
               
                 001 
                 AUGAT TERMINAL BARRIER ST 
                 P3 
               
               
                 001 
                 RELAY, SPST, PCB MOUNT T9 
                 K1 
               
               
                   
               
            
           
         
       
     
     Although the invention has been described with respect to a specific preferred embodiment thereof, many variations and modifications will immediately become apparent to those skilled in the art. For example, although the integrated defrost, electric heat control is shown and described as being disposed in the indoor unit it could, if desired, be placed in the outdoor unit as well. It is therefore the intent that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.