service manual for 12 vdc wall thermostat air
Contents
1. Thermostat Terminal Control and Supply Wiring Ceiling Assembly Terminal Wire OEM VENDOR Designation RorRED One Red 12 VDC Supply Wire to the N A Thermostat Two Blue One 12 VDC Supply Wire to the B or BLUE Thermostat and One Blue Wire to Ceiling B Assembly Plenum One Yellow Compressor Control Wire to L kd aw Ceiling Assembly Plenum GH or GREEN One Green High Fan Control Wire to Ceiling GH Assembly Plenum GL or GRAY One Gray Low Fan Control Wire GL W or WHITE One White 12 VDC Furnace Control Wire FURNACE from the Thermostat NOTE The W White wire is not available on COOL ONLY thermostats NOTE THE CONNECTING WIRES TO THE THERMOSTAT ARE PROVIDED BY THE VEHICLE MANUFACTURER OR INSTALLER THESE OEM OR VENDOR SUPPLIED WIRES MAY NOT BE COLOR CODED AS NOTED IN THE CHART ABOVE THE GROUND WIRE MUST BE A ZERO 0 RESISTANCE GROUND Thermostat Location Thermostats are very sensitive instruments For accurate temperature control and comfort the following considerations for thermostat locations should be taken into account 1 Locate the thermostat on an inside wall about five feet above the floor Pick a dry area where air circulation is good The thermostat should be mounted within a reasonable distance from the appliance the thermostat will control This will assure a more accurate temperature relationship between the thermostat and the appliance the thermostat will control 2 Do not install the2. 4 AIRXCEL A RV Products Division SERVICE MANUAL FOR 12 VDC WALL THERMOSTAT AIR CONDITIONING SYSTEMS ROOF TOP UNITS ONLY Airxcel Inc RV Products Division P O Box 4020 Wichita KS 67204 1976A376 1 11 TABLE OF CONTENTS I Introduction to Wall Thermostats 3 II Introduction to Relays 5 III Checking Ceiling Plenums with Individual Relays 7 IV Checking Ceiling Plenums with Printed Circuit Boards 8 V Diagnostic Flow Charts 13 VI Wiring Diagrams 17 WARNING SHOCK HAZARD To prevent the possibility of severe personal injury death or equipment damage due to electrical shock always be sure the power supply to the appliance is disconnected before performing any work on the appliance This can normally be accomplished by switching the breaker for the air conditioner to OFF disconnecting all external electrical connections and cords switching on board electrical generators and inverters to OFF and removing the cable from each positive terminal on all storage and starting batteries DANGER Some diagnostic testing may be done on energized circuits Electrical shock can occur if not tested properly Testing to be done by qualified technicians only The steps outlined in this manual are intended to guide the service technician through the pro
3. WIRING TO WALL nu THERMOSTAT TERMINALS INDICATED A BLUE A BLUE LI HI FAN gt RELAY a RR S Cc ORE SH Keen de a N M waj N M x 0 zilo a gH 8 GREEN 5 3 m m Lu Ze mI 5 ps S 5 m a a A GRAY YELLOW BLACK v WHITE 1 z E ER R V PRODUCTS INC z amp P O BOX 4020 am WICHITA KS 67204 SUPPLY WIRING PLUG CONNECTS TO UPPER UNIT SEE DIAGRAM SUPPLIED WITH UPPER UNIT 1976 147 FOR ADDITIONAL WIRING 17 7330 725 7330 726 amp 8330 725 Series Heat Cool Remote Free Delivery Ceiling Plenums W GL Y GH B FIELD WIRING TO WALL i it ft gt THERMOSTAT TERMINALS Powe Se Ed INDICATED BLUE ey e BLUE BLUE er ye DE i ver Se i 1 1 1 LO fb Er HIGH FAN gt 1 RELAY a i ie ft at E i oi ae 2 C P ii lu Sa a 0 Oz 1 i 1 M wj H I i H a em I 1 S zr z 3 E S Wl 1 YA l III GREEN zt thy YELLOW boa HEATER R RELAY 1 1 RE lt 1 d ax eae SE Ji 1 li al i d 2 g 1 1 5 1 1 in a 1 1 E GRAY Li E WHITE aie BLACK N PURPLE ba ORANGE 1 rj WHITE Se Bi WHITE H 1 1 E 1 1 E i med M a aup ZF a ORANGE 120 VAC 60 Hz 1 PH PLUG CONNECTS TO UPPER SUPPLY WIRING SWITCH UNIT SEE DIAGRAM SUPPLIED WITH UPPER UNIT 1976A171 FOR ADDITIONAL WIRING 18
4. to the control relays or a p c board which in turn energizes the air conditioner components or the furnace Note Relays and P C Boards will be discussed in Lesson II The following chart shows the different electrical connections made by the thermostat during operation The chart below assumes 12 VDC is supplied to the thermostat Red wire R and that 12 VDC or ground is supplied to the Blue wire B at all times Thermostat Operations Internal 12 VDC Connections Made Cool Mode Selected on Low Fan Red R to Yellow Y and Gray GL Cool Mode Selected on High fan Red R to Yellow Y and Green GH Heat Mode Selected on any Fan Speed Note Furnace Blower Operates Independently From Sequencer or Time Delay in Furnace Red R to White W Fan Only Selected Fan Only Selected Hi Fan Fan Only Selected Lo Fan Red R to Green GH Analog Red R to Green GH Digital Red R to Gray GL Digital Note When the auto cool mode is selected on the thermostat the fan cycles on and off with the compressor as needed When the on cool mode has been selected the fan runs continuously and the compressor cycles on and off as needed The following chart depicts thermostat wiring and the wiring destinations for air conditioners with control boxes containing printed circuit boards
5. CEILING PLENUMS WITH PRINTED CIRCUIT BOARDS Most of the 7000 and 8000 series ceiling plenums built since 1992 have printed circuit boards instead of individual relays Printed circuit boards are less costly and require less wiring The printed circuit boards all have relays mounted permanently on them Even though the boards may look much more complicated they are very easy to troubleshoot On the following pages you will find some visual aids that will help you troubleshoot these units without removing the thermostat or the air conditioner control box lid Airxcel Inc has and is building many ceiling assembly packages which use printed circuit boards to control air conditioner system functions Just like the individual relays the printed circuit board must receive a signal from the wall thermostat to operate A common ducted ceiling assembly application is shown in Figure 4 on page 9 SUPPLY AIR DUCT MOUNTING FRAME amp BOLTS CEILING DUCT DIVIDER SUPPLY AIR PLATE SUPPLY AIR GRILLS TIGHTEN UNTIL GASKET j INDICATING TAB TOUCHES ROOF ta D MOUNTING BOLT MOUNTING BOLT Laser TIGHTEN UNTIL COMPRESSION i SPRING CLOSES 1 FILTER GRILLE WASHER ST jn TAB METHOD OR COMPRESSION SPRING METHOD zA 2 FIGURE 4 Control Box Assembly Electrical Insulator Electrical Box Cover Printed Circuit Board Freeze Thennister FIGURE 5 Note In ducted applications similar to the
6. ay coil When the thermostat switch is placed in the cool position 12 VDC travels from the thermostat red wire to the thermostat yellow Y wire and then to the relay coil When the coil is activated an electromagnet inside the relay will pull the contacts closed The 115 VAC will now operate the compressor until the thermostat opens or the system switch is turned to the off position Figure 1 shows a very simplified control circuit for compressor operation only The entire control circuit for the air conditioner heating system would include the rest of the thermostat functions and possibly 2 or 3 more relays In addition to the compressor relay you would need a separate relay for Low Fan one for High Fan and possibly one for Heat if a heat pump or electric heating element is used Please refer to the previous lesson or refer to Figure 1 for proper wiring from the wall thermostat to each individual relay 115 VAC L2 LI Thermostat 12VDC Y yellow compressor 12VDC thermostat B blue Compressor FIGURE 1 III CEILING PLENUMS WITH INDIVIDUAL RELAYS Airxcel Inc built two types of ceiling assembly packages which incorporate individual relays for the air conditioner system functions Line drawing examples of these two ceiling assembly types are shown in Figures 2 and 3 Low Voltage Thermostat Wiring Entrance 720 amp 726 Free Delivery Ceiling Plenums Relays located in this area K 115 VAC Supply Wiri
7. cess of correctly diagnosing a Coleman Mach series roof top air conditioner with a remote wall thermostat control system I INTRODUCTION TO WALL THERMOSTATS All of the air conditioning functions are controlled by the wall mounted thermostat These thermostats utilize a 12 VDC electrical circuit which is supplied by the vehicle manufacturer or the installer of the air conditioning unit Most of the thermostats provided by Airxcel Inc are combination Heat Cool thermostats These thermostats are capable of operating both the roof top air conditioner and any furnace with a 12 VDC control circuit The figures below list three of the most commonly found Coleman Mach wall mounted thermostats for roof top air conditioners heat pumps excluded These thermostats are listed in chronological order from the oldest to the newest Mechanical By Metal Thermostats Heating anticipator EE 8 000004 THERMOSTAT BASE By Metallic coil Electronic Thermostats Electronic Digital Display Thermostats o 60 70 80 90 mac ZUlac4 amp FAN OFF cooL 4 1 Te HEAT mona j prion off e aaa gt gt Auto on Cool 4 rHeat Lo Hi n AUTO is ON E SYSTEM FAN EES FAN MODE THERMOSTAT FAN SPEED _ NOTE ALL THREE OF THESE THERMOSTATS ARE COMPLETELY INTERCHANGEABLE Thermostats are really nothing more than temperature controlled switches When the need for cooling or heating exists the thermostat sends a 12 VDC signal
8. he freeze thermistor opens if the evaporator coil temperature drops below 32 F and closes at 55 F The probe end of this switch should be found pushed into the fins of the evaporator coil and the wires are hooked to the printed circuit board It is okay to remove the thermistor wire from the board and jump around these terminals for diagnostic purposes If the air conditioner compressor is running and NO VOLTAGE is found between terminals Y and B on the low voltage terminal strip the printed circuit board must be replaced The compressor relay has evidently welded shut In conclusion you can save a lot of time if you get in the habit of going immediately to the ducted control box assembly for troubleshooting purposes There in a matter of minutes you can tell if the problem is in the thermostat the printed circuit board or the upper unit 12 Note V DIAGNOSTIC FLOW CHARTS When working with the following diagnostic flow charts start at the top left corner and work towards the the right or down the page as applicable Do not skip around or start in the middle without performing all prior steps DANGER The following diagnostic testing will be done on energized circuits Electrical shock can occur if not tested properly Testing to be done by qualified technicians only 13 No High Fan Operation Thermostat in the FAN ONLY or HIGH COOL position Start Here j Check for 12Vdc between GH and B Check for 12Vdc be
9. ng Roof Top Unit Grounding Lug Ground 115 VAC Su Wiri Sa Strain Da i Cut Out Of The Ceiling Roof Top Unit Plug i Connection Assembly Air Chute FIGURE 2 6799 730 Series Ducted Ceiling Plenums Low Temperature Switch Electrical Box Relays x3 Electrical Box Cover High Voltage Area FIGURE 3 7 The following charts depict the thermostat control wiring ceiling assembly wiring destinations and relay functions for air conditioners with control boxes containing individual relays 6799 720 amp 726 Series 7330 720 amp 726 Series Ceiling Plenums Thermostat Ceiling Plenum Wire Unit Operation Yellow Y Yellow Compressor Relay Green GH Green High Fan Relay Gray GL Gray Low Fan Relay Blue B 12 VDC Blue N A White W White Furnace or Heat Element Relay 6799 730 Series Ceiling Plenum Thermostat Ceiling Plenum Wire Unit Operation Yellow Y Black Compressor Green GH Green High Fan Gray GL Gray Low Fan Blue B 12 VDC Blue N A White W White Furnace or Heat Element Relay The low voltage wiring connections for these control systems are hard wired by the manufacturer or installer of the unit and they may not all use color coded wire as noted above Note If the heating system includes a gas fired furnace the thermostat white wire will energize the furnace control circuit Usually a time delay relay located at the furnace IV
10. one found in Figure 4 the printed circuit board control box assembly is found mounted in the return air opening of the air conditioner In some older applications the printed circuit board control box assembly will be located in the center of the roof opening just above the return air grille Figure 5 shows an exploded view of the Control Box Assembly CHECKING THE THERMOSTAT OPERATION The 12 VDC signal from the wall thermostat may be checked at the Low Voltage Terminal Strip Figure 6 located externally on the ceiling plenum wiring box EVAPORATOR FREEZE SENSOR White Black ees wl Electric Heat YELLOW BLUE COMPRESSOR 12 voc Su GREEN LOW SPEED FAN HIGH SPEED FAN FIGURE 6 10 Any time the thermostat is placed in the FAN ONLY position you should be able to read 12 VDC between terminals GH and B at the Low Voltage Terminal Strip using an Analog Thermostat See Figure 6 Digital will be between GL amp B Any time the thermostat is placed in the LOW COOL position you should be able to read 12 VDC between terminals GL and B for the Low Fan and between terminals Y and B for Compressor operation Any time the thermostat is placed in the HIGH COOL position you should be able to read 12 VDC between terminals GH and B for the High Fan and between terminals Y and B for Compressor operation Note Thermostat operation in the Heating Mode cannot be tested at the Ceiling Assembly Low Voltage Terminal Strip if the the
11. ostat Yes Yes Check for 12Vdcat the furnace N Ye sa Ifit is an electronic Ifit is a mechanical thermostat them ostat check to replace the them ostat see ifthe 2 amp fuse in the back ofthe No them ostat is open Problem is not wth the Thermostat Refer to Furnace manufacturers Troubleshooting guidelines Yes Check wiring between Replace the 2 amp fuse Thermostat and furnace za check for ren in Replace the thermostat Thermostat wiring and Control circuit 15 No Compressor Operation Thermostat in Cool Position and Temperature Control set below room temperature Start Here ji Check for 12Vdc between Y amp B at lowvoltage s E ss d e No Check for 12Vdc between the No Restore 12Vde EDL at the ceiling assembly junction box Thermostat Red and Blue wires To the thermostat Yes Yes Check for 12 Vdc between the 0 Check for 115Vac between the purple Thermostat Yellow and Blue wires And yellow vires Pins 1 amp 3 on the 9 pin Plug connector at the ceiling assembly junction Ye Box See Figure 7 si Check the wiring between thermostat Yes No And air conditioner ceiling assem bly Check wiring to upper unit Check compressor run Check for 115Vac between black and Capacitor Check start White incoming pover wires of black and capacitor relay Check White lug terminals on the PC board Compressor windings for open Or ground Check compressor For mechanically locked up Ifi
12. rmostat is operating a gas fired furnace Note The wall thermostat will be equipped with an optional Electric Heat Gas Heat switch if the recreational vehicle is equipped with a Heat Pump or with an Electric Heating Element In this case the Electric Heat Mode may be checked on the Low Voltage Terminal Strip In either case the Low Voltage Terminal Strip will have an additional terminal labeled W for electric heating operation When Electric Heat is chosen at the thermostat you should be able to read 12 VDC between terminals W and B Thermostat Ceiling Assembly Terminal Unit Operation Yellow Y Y Compressor Green GH GH High Fan Gray GL GL Low Fan Blue B 12 VDC B N A White W W Electric Heat If you do not find voltage at the Ceiling Assembly Low Voltage Terminal Strip as described above the problem needs to be traced back to the thermostat or the vehicles low voltage wiring CHECKING THE PRINTED CIRCUIT BOARD OPERATION Low voltage MUST be verified at the low voltage terminal strip as described earlier in this text or as noted in the chart below before proceeding to the next step or checking the printed circuit board In order to continue you must first verify the 115 VAC power source to the air conditioner control box assembly If the 115 VAC power source is NOT present all of the air conditioner functions will be dead and power must be restored to continue 115 VAC power must be present to
13. t is an electronic thermostat check To see ifthe 2 amp fuse in the back of The thermostat is open If it is a mechanical thermostat Replace thermostat Replace fuse and check for Short in therm ostat wiring No Replace thermostat Yes And control circuit Restore 115Vac to air conditioning unit Bridge across freeze thermistor terminals on No Check wiring in the control box then if compressor relay PC board Does compressor come on and run Will not make with them istor jumped replace PC board Yes If com pressor runs when circuit is bridged Check the E vaporator Coil for freeze up Replace the PC Board ifthe freeze Sensor checks good for continuity Yes Warm coil to above 60 F if compressor relay still No Will not make with freeze sensor installed Check Replace sensor if wre The freeze sensor for continuity Broken or continuity failure VI WIRING DIAGRAMS 7330 735 7330 736 amp 8330 735 Series Heat Cool Ducted Ceiling Plenums UNIT PLUG TO WALL THERMOSTAT SEE DIAGRAM SUPPLIED ON UPPER UNIT FOR ADDITIONAL WIRING Se COIL SENSOR o G LOW FAN RELAY THERMISTOR HIGH FAN RELAY HEATER PLUG P C BOARD HEATER SUPPLY WIRING 19768196 7330 720 amp 8330 723 Series Cool Only Remote Free Delivery Ceiling Plenums Y GL GH B FIELD
14. the printed circuit board if any one of the air conditioner functions are working The operation of the printed circuit board may be checked at the High Voltage 9 Pin Connector Figure 7 without removing the electric box lid The chart below shows the 115 VAC connections made by the printed circuit board to the High Voltage 9 Pin Connector Thermostat Connections at the Low 115 VAC Connections Made Between Voltage Terminal Strip Terminals at the 9 Pin Connector 12 VDC at Y and B Terminals 1 and 3 12 VDC at GH and B Terminals 5 and 9 12 VDC at GL and B Terminals 6 and 9 11 FIGURE 7 Note To check voltage at the 9 pin connector plug it may be necessary to unplug the upper unit from the control box If the air conditioner is still not functioning and both 12 VDC and 115 VAC are present and accountable at their proper locations the problem is located in the upper unit If the correct 115 VAC connections are NOT made at the 9 pin connector plug after 12 VDC power is applied to the low voltage terminal strip the problem is in the printed circuit board with one exception as described below The low temperature freeze thermistor will de energize the compressor relay coil on the printed circuit board if the air conditioner evaporator coil starts to freeze If this happens you would still have 12 VDC at terminals Y and B but no voltage would be present at terminals 1 and 3 in the High Voltage 9 Pin Connector T
15. thermostat where there are unusual heating conditions such as direct sunlight heat producing appliances television radio wall lamp etc or a furnace or air conditioner supply register 3 Note When installing or servicing these thermostats the technician should take all necessary precautions not to short any positive wire to ground Permanent damage to the thermostat may occur Make sure all connections are good and tight Loose connections may cause relay chattering which leads to welded relay contacts on air conditioner printed circuit boards II INTRODUCTION TO RELAYS In the previous chapter on thermostats we learned the wall thermostat makes necessary connections that provide low voltage power to initiate all of the air conditioning or heating functions There is one question left unanswered How de we use this 12 VDC power to operate a 115 VAC appliance THE ANSWER IS We use relays or printed circuit boards with relays located on them How Do Relays Function As the coil is energized in the relay it will open or close a set of contacts capable of carrying high voltage and 115 VAC in this case All of our control circuit relays are normally open and the contacts close as power from the thermostat is applied As shown in Figure 1 on page 6 the 115 VAC power to the compressor is interrupted by a set of normally open contacts on the relay In order for these contacts to close 12 VDC must be applied by the wall thermostat to the rel
16. tween No No At the lowvoltage terminal strip in the The thermostat Red and Restore 12Vdc Ceiling assembly See Figure 6 Blue wires To the thermostat Yes Yes Check for 115Vac between the Black and white wires pins 5 amp 9 on Check for 12Vdc between Green No The 9 pin connector plug at the No And Blue wires at the thermostat Ceiling assem bly junction box See Figure 7 Check wiring to upper unit Check fan capacitor Check fan Motor windings for open or Ground Check motor bearings Check wiring between thermostat And upper unit Ifit is a mechanical thermostat Replace the thermostat a Ifit is an electronic Thermostat check to see if Yes Check for 115Vac between black Yes The 2 amp fuse is open on And white incoming pover wires or The back ofthe thermostat Lug terminals on PC board No Replace the Thermostat Restore 115Vac power Ensure all wires and electrical Connections are intact repair as Replace fuse and check for possible Needed If everything is OK Short in wiring or control circuit Replace the PC board Note To check voltage at the plug it may be necessary to unplug the upper unit from the wirebox 14 No Furnace Operation Thermostat in Heat Position and Temperature Control set above room temperature Start Here j Check for 12Vdc between White No Check for Kc between No Restore 12Vdc to The thermostat Red and And Blue wires at the thermostat Blue wires The therm
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