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Duo-Therm 39125 Service Manual

Duo-therm air conditioners & heat pumps service manual
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AIR CONDITIONER & HEA
AIR CONDITIONER & HEA
AIR CONDITIONER & HEA T PUMP
AIR CONDITIONER & HEA
AIR CONDITIONER & HEA
This Service Manual is the result of the dedication of The Dometic Cor-
poration and its engineers to providing service people the necessary
instructions for making accurate analysis of certain conditions. Provided
is a comprehensive guide designed to lead a qualified mechanic through
the Service Manual to locate and solve symptoms that may occur.
Dometic continues their commitment to providing the most up to date
information about servicing Duo-Therm Air Conditioners and Heat Pumps.
Form No. 3108892.013 10/00
©2000 The Dometic Corporation
LaGrange, IN 46761
SERVICE MANU
SERVICE MANU
SERVICE MANU AL
SERVICE MANU
SERVICE MANU
T PUMP
T PUMP
T PUMP
T PUMP
AL
AL
AL
AL

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Summary of Contents for Duo-Therm 39125

  • Page 1 Service Manual to locate and solve symptoms that may occur. Dometic continues their commitment to providing the most up to date information about servicing Duo-Therm Air Conditioners and Heat Pumps. Form No. 3108892.013 10/00 ©2000 The Dometic Corporation...
  • Page 2 Table of Contents Section Page Installation ................. A ........1 AC Power Requirements ..........A1 ........ 1 DC Power Requirements ..........A2 ........ 1 Field Wiring ..............A3 ........ 1 Breaker ................. A4 ........ 2 Airbox ................A5 ........ 2 Ducting System .............
  • Page 3 Section A - Installation A1. AC Voltage If a furnace is to be operated by the Analog Control Sys- tem, the furnace thermostat leads are connected to the The unit is a 115VAC, 60Hz appliance. The proper operat- blue/white striped wires out of the Analog Control Box. The ing range is between 103 and 126.5 volts AC.
  • Page 4 1. 579 & 600 Series 17.5 sq. in. 2. 591, 595 & 630 Series 21.0 sq. in. MODELS CIRCUIT PROTECTION T.D. Fuse HACR Breaker Duct Sizing Requirements as Follows: 39125 (Basement) 15 amp 15 amp Min. Max. 39325 (Basement) 20 amp 20 amp Duct Depth (591/595/630 Series) 1-1/2"...
  • Page 5 These items must be determined in conjunction with the Air Distribution System Sizing and Design Requirements listed. Duo-Therm’s return air kits are designed to be installed Note: Alternate configurations and methods may be used tightly to the bottom of the base pan and ceiling template.
  • Page 6 A6a. Roof Top Units Section A - Installation, cont’d. Route a copper 12 AWG, with ground, 115 VAC supply line FIG. A6 from the fuse or circuit breaker box to the roof opening. a. This supply line must be located in the front portion of the 14-1/4"...
  • Page 7 See FIG. A9. Another method of connecting the discharge air to the coach’s main duct used Duo-Therm’s return air kit. It uses half of the 14-1/4" x 14-1/4" (±1/8") opening as a discharge plenum. If the duct opening is not clean, restriction of air can cause the coil to freeze.
  • Page 8 See FIG. A12. free area; however some manufacturers use their own grills. Duo-Therm has available a quick cool return air kit that will If a manufacturer’s grill is used, it must use the above for- allow the cooled air to come directly out of the air condi- mula to make sure the return air is sufficient to reduce the tioner.
  • Page 9 The control system used by Duo-Therm Air Conditioner is designed with a low temperature switch that will shut off the compressor and allow air to flow through the coil to melt the frost.
  • Page 10 A6a. Roof Top Units Section A - Installation, cont’d. FIG. A19 Freeze Control Installation Freeze Control Installation 579, 590 & 595 Series: 600 Series: a. Snap freeze control into place on return bend located a. Snap the freeze control into place on return end lo- at left side of evaporator coil as follows: cated at right side of evaporator coil as follows: 1) Locate “D”...
  • Page 11 “D” slot in the coil header. Clearances A6b. Basement Units The minimum clearances to the evaporator are zero inches Models 39335 and 39125 to the bottom, top, left and right sides. Access to the elec- Outdoor Section: trical connections and drain connection must be provided The Condenser coil is designed to have a fresh supply of when making the installation.
  • Page 12 A6b. Basement Units Section A - Installation, cont’d. RETURN RISER X 2 FIG. A22 2" X 12" INSULATED DUCT (MIN.) 90 SQ. IN. FILTERED (MIN. X 2) DISCHARGE 2" X 10" CLOSEABLE CONDENSER GRILL (MIN. X 4)) FLOOR CUTOUT 90 SQ. IN. MINIMUM SUPPLY AIR INSULATED FLOORING...
  • Page 13 A6b. Basement Units Section A - Installation, cont’d. FREE AREA - is the opening that remains in a grill or lou- Clearances vered panel after the restrictions are taken away. For ex- The air conditioning unit clearances depend on: ample, an opening of 10 x 20 inches has 200 square inches. 1.
  • Page 14 Section A - Installation, cont’d. Grills FIG. A25 Note: The Return air grill must have the same square sur- face as the return air duct. 1. For each air conditioning system, there must be a re- turn grill to bring cabin air back into the unit. There must also be at least four discharge grills per unit.
  • Page 15 Section A - Installation, cont’d. When the floor plan or interior design of an RV changes, Dometic suggests trying several locations for the thermo- stat or remote sensor to determine the best location for mounting. Both heating and air conditioning should be tested, especially when using different duct systems and the same thermostat.
  • Page 16 The recreational vehicle manufacturer has equipped the lect the fan speed that best satisfies your needs. See FIG. vehicle with Duo-Therm’s Air Conditioner. The ability of the unit to maintain the desired inside temperature depends a. HIGH COOL - Selected when maximum cooling on the heat gain of the RV.
  • Page 17 B1b. Bimetal Relay Controls Section B - Operation, cont’d. Special Feature Cooling Operation Place the Temperature Set Lever to desired temperature When thermostat: level (located at top of thermostat). Select fan speed that Heat/Off/Cool Switch is in the OFF or HEAT position and Auto/On Switch is in the ON position, the air con- best satisfies your needs: (upper right switch at bottom of thermostat).
  • Page 18 B1d. Comfort Control Center Section B - Operation, cont’d. Analog Control Electric Heat Strip Operation ditioning and gas heating appliances. When you begin to (If unit is equipped with optional electric heat strip.) first operate the Comfort Control Center, you will see that 1.
  • Page 19 Cooling Mode Operation - See FIG. B4 & B5 it a “head start” on the expected high outdoor ambient will (To set cooling temperatures and fan speeds on Duo-Therm greatly improve its ability to maintain the desired indoor Air Conditioners and the cooling mode of Duo-Therm Heat temperature.
  • Page 20 Cooling Mode Operation 1. Begin by placing the power switch on the lower right (To set cooling temperatures and fan speeds on Duo-Therm hand edge of the Control Center in the ON position. Air Conditioners and the cooling mode of Duo-Therm Heat To do this, simply move the lever to the right.
  • Page 21 The final selected SETPOINT trol Center. will be displayed in the LCD area of the Comfort Con- 4. The Duo-Therm heat pump system will not operate trol Center. when the Comfort Control System is in the FURNACE 4.
  • Page 22 4 in the LCD readout. FIG. B10 Stage Control Operation If the vehicle is equipped with a Duo-Therm Dual Base- ment Air Conditioner or a Dual Basement Heat Pump, you have an air conditioning system that is designed to opti- mize comfort and running efficiencies.
  • Page 23 34°F, the control will return to the HEAT PUMP operation. If your vehicle does not con- tain a furnace, and you have a Duo-Therm Heat Pump, once the outside ambient temperature goes below 24°F, the system will shut down until the outside temperature reaches 34°F, at which time the Heat Pump will resume...
  • Page 24 Section B - Operation, cont’d. B2. Heat Pump Reset General Information If the Comfort Control Center is not operational, inadequate The roof-top heat pump was designed to operate in a MILD data or no functions occur, reset the Comfort Control Cen- GEOGRAPHICAL AREA for heating where the heat loss is ter to factory settings.

  • Page 25: Heating Mode

    B2. Heat Pump Section B - Operation, cont’d. The Heating Mode leaves the outside coil as high pressure liquid. To heat the air inside a structure, heat is removed from the As the high pressure liquid R22 leaves the outside coil outside air or ambient and released to the inside air.
  • Page 26 B2. Heat Pump Section B - Operation, cont’d. The high pressure liquid R22 enters the outside coil in a Fan Operation: controlled amount from the capillary tube. When the liquid This will circulate the air in your RV without cooling or heat- enters the low pressure atmosphere of the outside coil ing.
  • Page 27 B2. Heat Pump Section B - Operation, cont’d. B2c. Analog Control System FIG. B18 In order to familiarize yourself with the operation of the Analog Control System, the following diagrams along with the accompanying text will explain all the functional char- acteristics of the system.
  • Page 28 B2. Heat Pump Section B - Operation, cont’d. B2d. Comfort Control Center Analog Control Electric Heat Pump Operation - See FIG. B19 The Comfort Control Center has been designed for you to easily operate all the air conditioning and gas heating ap- 1.
  • Page 29 Section C - Components C1. Motors To check the motor, turn the unit circuit breaker OFF. With an AC voltmeter, verify that the circuit has no AC voltage. Roof Top Units - To check the motor, turn the unit circuit Next, locate the electric box and remove its cover.
  • Page 30 Section C - Components, cont’d. Lack of continuity between the white wire and any of the the VOM meter to the highest ohm scale and connect the other wires indicates an open circuit and requires that the probes to the capacitor terminals. The reading should rap- motor be changed.
  • Page 31 Section C - Components, cont’d. C5. Compressor The start capacitor must be manually discharged. Using an AC voltmeter set at the 500 volt scale or higher, connect To check compressor, turn the air conditioner circuit breaker meter leads to the terminals of the capacitor. Next, discon- to OFF.
  • Page 32 Section C - Components, cont’d. C6. Overload Protector C7. Cold (Freeze) Control An overload protector is a component that will open the AC (Low Temperature Protection Device) circuit to the compressor if the compressor overheats due The cold (freeze) control is used on roof top air condition- to an electrical problem.
  • Page 33 Section C - Components, cont’d. C9. Selector Switch C9b. Selector Switch - Roof Top Heat Pump C9a. Selector Switch - Roof Top Air The selector switch in a mechanical heat pump has sev- Conditioner eral positions. The various switch positions can be tested The selector switch in a mechanical air conditioner has for continuity with a volt/ohm meter set on the highest scale.
  • Page 34 Section C - Components, cont’d. C10. Changeover Thermostat Model 59126.502, 630025 First, turn the 20 amp air condi- tioner breaker to OFF. Next, remove the wires from the The changeover thermostat is a capillary tube/bellows-type switch. With the switch in the OFF position, you should not switch.
  • Page 35 Section C - Components, cont’d. C12. Ambient Sensor For the specific temperature surrounding the sensor, the ohms reading should be as follows: The ambient sensor is the outside air temperature sensor and is used on heat pump units only. This component al- Room Temperature Ohm Reading lows the heat pump to operate down to 24°F.
  • Page 36 20 volt-amps. The reversing valve’s solenoid can be energized in either HEAT or COOL mode of operation. Most Duo-Therm Heat To check the transformer, first verify AC voltage is to the Pumps have the solenoid energized in the COOL mode of line terminals.
  • Page 37 Section C - Components, cont’d. C16. Relays C16c. Relay, SPST (single pole/single throw) is used on Models C16a. Time Delay Relay 39115.602, 39115.616 and The time delay relay is used on Model 39424.601. Its pur- 39115.626. pose if to provide a thirty second delay of power to Circuit 2 System after Circuit 1 System.
  • Page 38 39424.601, it opens the control circuit for the fan motor circuit to Circuit 2 compressor. On Models 39115.626, when the coil is energized. 39125.601, 39335.601 and 39335.636 it is a furnace blower relay. Note: Incorrect wiring to the thermostat can energize the relay coil on heat pump models 39325.XXX, 39335.XXX...
  • Page 39 C16i. Relay, 2-Pole Furnace Blower tor. The relay is used on basement air conditioner Model 39125 When COOL, OFF and HEAT PUMP modes are selected, and Basement heat pump Model 39335 ONLY. The relay the relay coil is not energized. When AUX HEAT mode is has five (5) terminals.
  • Page 40 Section C - Components, cont’d. C17. Printed Circuit Boards C16l. Relay, DPST (double pole/ single throw) is used on Mod- C17a. Circuit Board for Bi-Metal els 390XX.XXX. Thermostat It controls the compressor. The relay board consists of a transformer, compressor re- The relay has a 24 volt AC coil.

  • Page 41: Control Box

    AC circuits that control the operation of nal 3. If the circuit is completed the bulb will illuminate. the Duo-Therm Unit. Note: DO NOT use a voltmeter to do these checks as it 1. Air Conditioners will give erroneous readings.
  • Page 42 Section C - Components, cont’d. 4. Basement Heat Pump module board, you would first disconnect the 6-pin plug To verify circuits are being completed by the Analog Con- connector from the electric kit. trol Board, you must remove the cover of the unit electrical box.
  • Page 43 Section C - Components, cont’d. Using a 115 volt incandescent bulb, check from AC white FIG. C37 (common) of incoming 115V AC; one lead from incandes- cent bulb and the other lead from incandescent bulb to the terminals listed below to determine if a particular circuit is completed through the board.
  • Page 44 Plug the thermostat cable into the thermostat connector cable. There are four types of thermostats used on Duo-Therm When an auxiliary furnace is used with the heat pump, a units. Each type is explained in this section.
  • Page 45 Section C - Components, cont’d. Before checking the thermostat for operation, first deter- FIG. C42 mine that the thermostat is receiving DC power from the relay board then disconnect the cable assembly from the back of the thermostat. Next, use a DC voltmeter and check from red wire or Pin 2 on cable assembly (positive [+] lead from voltmeter) to brown wire or Pin 7 (negative [-] lead from voltmeter).
  • Page 46 Section C - Components, cont’d. With System Switch in OFF, Fan Switch in HI ON and room FIG. C43 temperature ABOVE or BELOW setpoint temperature, you should have continuity between red wire (Pin 2) to black wire (Pin 4) and blue wire (Pin 6). You should NOT have continuity between red wire to violet, white or yellow wires.
  • Page 47 Section C - Components, cont’d. FIG. C44 A three connector cable 18 to 22 AWG is to be used for low voltage connections. Low voltage wires in the control com- partment are marked “R”, “G” and “Y”. Route low voltage cable from thermostat to unit electrical box.
  • Page 48 Section C - Components, cont’d. between RC to Y and RC to G. With FAN switch to ON To check ACTIVE terminals, place one lead from ohm meter to R terminal and the other lead to the ACTIVE terminal. position, continuity should exist between RC to G regard- less of room temperature.
  • Page 49 Section C - Components, cont’d. Models 39025.502, 39035.601, 39045.601 & 39045.616 With the SYSTEM switch in OFF position and the FAN The thermostat is a 24V AC controlled system and is a switch in AUTO position, no continuity should exist R to Y, bimetal type.
  • Page 50 Section C - Components, cont’d. Models 39115.601, 39115.602, 39115.616 & 39115.626 The thermostat is a 12V DC controlled system and is a FIG. C50 bimetal type. It has three (3) switches on the face of the thermostat. On the left side there is a SYSTEM switch and on the right side there are two FAN switches.
  • Page 51 Section C - Components, cont’d. With the room temperature below the setpoint tempera- SWITCH IF ROOM TEMP. TERMINALS THAT ture, continuity should exist between RC to G. No continu- COMBINATION IS ABOVE/BELOW ARE “ON” ity should exist between RC to Y, RC to H and RH to W. SYSTEM SETPOINT TEMP.
  • Page 52 There are 3 different Analog thermostats being used to ture, you should have continuity between red wire (Pin 2) control Duo-Therm Air Conditioners, Air Conditioners with to black wire (Pin 4). You should NOT have continuity be- Heat Strips, and Heat Pumps. The type of Thermostat used tween red wire to violet, white, yellow or blue wires.
  • Page 53 Section C - Components, cont’d. Early Model Terminal Identification Early Model Color Coding Check for voltage between the GND terminal and: 1. Connect the previously run +12V DC to the red wire 1. FAN terminal for voltage ranging from 8.38 to 17.31 labeled +12V protruding from the relay kit.
  • Page 54 Section C - Components, cont’d. C18d. Comfort Control Center™ C19. Cable Assembly The Comfort Control Center is the component that makes The ten (10) wire cable is used with remote wall mounted all decisions for operation depending on the system and thermostats.
  • Page 55 Section C - Components, cont’d. Two through Eight Wire Cables FIG. C56 The Bi-Metal, Analog and Comfort Control Center controls require a 18 to 22 AWG cable for DC power and control of various components. The cable can be two through eight wires.
  • Page 56 Section C - Components, cont’d. Model 39325.XXX and 39335.XXX (Heat Pumps) Model 39424.601 (Heat Pump) The cable assembly is a ten-wire cable with seven of the The cable assembly is a ten wire cable with seven of the ten wires used. The thermostat end has a 10-pin flat con- ten wires used.
  • Page 57 Section C - Components, cont’d. C20.Sealed System C20b. Recharging Note: The Clean Air Act of 1990 set guidelines in regard C20a. Filter Drier & Capillary Tube to recapturing or disposition of refrigerants. Check with lo- One mechanical problem you may encounter is refrigerant cal authorities for proper handling or evacuation of refrig- flow restriction.
  • Page 58 Section C - Components, cont’d. Next, weld the process tube in place. We recommend a FIG. C63 brazing material which melts between 950° and 1450° Fahr- enheit, and contains a minimum of 2% silver and 5% to 10% phosphorous. This FIG.
  • Page 59 Section C - Components, cont’d. Now the blue low side and the red high side lines should air temperature to the condenser (hot) coil. be disconnected. Make sure that the air conditioner con- 2. Add 32°F to the above thermometer reading. nection is sealed before removing the lines.
  • Page 60 Section C - Components, cont’d. 21. Wiring Example: Typical Wiring Diagram for Roof Top Heat Pump Note: Be sure to use the wiring diagram on the appli- ance for the specific unit you are diagnosing. On rooftop units there is a 6-pin connector. Verify that all wires are tight in this connector and to all components.
  • Page 61 Section C - Components, cont’d. C22. Other The air conditioner must not be installed in a valley on the roof; water may pool around the drain holes and be drawn C22a. Ambient Temperature into the air conditioner. Running the air conditioner or heat pump at a temperature Make sure the air conditioner is tightened to the specifica- below 75 degrees Fahrenheit may cause the inside coil tions.
  • Page 62 Section D - Configuration Ducted Installations FIG. C69 Short cycle could be caused by air being circulated directly on the remote sensor. Make sure you do not have a regis- ter too close to the remote sensor. Verify the duct connec- tion at the unit is not leaking into the return air.
  • Page 63 Section D - Configuration, cont’d. 1. One Comfort Zone FIG. D4 One Rooftop Air Conditioner To configure one rooftop air conditioner, all Dip switches are to “OFF” position and the cold (freeze) control is plugged into P5 (blue) connector. Two thermostat wires from the furnace, communications line, AC power and DC power are properly connected to the air conditioner control box.
  • Page 64 Section D - Configuration, cont’d. One Rooftop Heat Pump Plus One Gas Furnace Note: If a remote sensor is used, it must be plugged into To configure one rooftop heat pump plus one gas furnace, the P4 (white) connector. all Dip switches are OFF. The freeze control is NOT used. The blue connector must stay open (P5).
  • Page 65 Section D - Configuration, cont’d. One Basement Air Conditioner Plus One Gas Furnace Note: If a remote sensor is used, it must be plugged into the P4 (white) connector. To configure one basement air conditioner plus one gas furnace, all Dip switches are OFF. Two thermostat wires from the furnace, AC power, DC power and communica- tion line are properly connected to the heat pump elec- tronic control box.
  • Page 66 Section D - Configuration, cont’d. One Basement Heat Pump Plus One Gas Furnace Note: If a remote sensor is used, it must be plugged into To configure one basement heat pump plus one gas fur- the P4 (white) connector. nace, all Dip switches are OFF. The ambient sensor is plugged into the proper connector (red).
  • Page 67 Section D - Configuration, cont’d. One Dual Basement Air Conditioner Plus One Gas Furnace Note: If a remote sensor is used, it must be plugged into To configure one dual basement air conditioner plus one the P4 (white) connector. gas furnace, the STAGE Dip switch on AC power module for Circuit 2 must be turned to ON.
  • Page 68 Section D - Configuration, cont’d. One Dual Basement Heat Pump Plus One Gas Furnace Note: If a remote sensor is used, it must be plugged into To configure one dual basement heat pump plus one gas the P4 (white) connector. furnace, the STAGE Dip switch on AC power module board for Circuit 2 must be turned to ON.
  • Page 69 Section D - Configuration, cont’d. 2. Two Comfort Zones ZONE 2 configuration should have Dip switch 5 (ZONE Two Rooftop Air Conditioners Plus One Gas Furnace 2) in the ON position and all other Dip switches in the To configure two rooftop air conditioners plus one gas fur- OFF position.
  • Page 70 Section D - Configuration, cont’d. FIG. D27 COMMUNICATIONS LINE ZONE 1 configuration should have Dip switch 1 (heat Two Rooftop Air Conditioners with Heat Strip Plus One strip) to ON position and all other Dip switches to OFF Furnace position. The cold (freeze) control should be plugged To configure two rooftop air conditioners with heat strip into P5 (blue) connector on the AC power module.
  • Page 71 Section D - Configuration, cont’d. ZONE 1 configuration should have Dip switch 1 (heat Note: If a remote sensor is used, it must be plugged into strip) to ON position and all other Dip switches to OFF the P4 (white) connector. position.
  • Page 72 Section D - Configuration, cont’d. One Rooftop Air Conditioner Plus One Rooftop Heat Pump ZONE 2 (Air Conditioner) configuration should have Plus One Gas Furnace Dip switch 5 (ZONE 2) to ON position and all other Dip To configure one rooftop air conditioner plus one rooftop switches to OFF position.
  • Page 73 Section D - Configuration, cont’d. FIG. D34 Two Rooftop Heat Pumps Plus One Gas Furnace ZONE 1 configuration should have all Dip switches to To configure two rooftop heat pumps plus one gas furnace, OFF position. The cold (freeze) control is NOT used. ZONES need to be established.
  • Page 74 Section D - Configuration, cont’d. Note: If a remote sensor is used, it must be plugged into ZONE 2 configuration should have Dip switch 5 (ZONE 2) to ON position and all other Dip switches to OFF the P4 (white) connector. position.
  • Page 75 Section D - Configuration, cont’d. Two Basement Air Conditioners Plus One Gas Furnace ZONE 1 configuration should have all Dip switches to To configure two basement air conditioners plus one gas OFF position. furnace, ZONES need to be established. For explanation purposes, the front unit will be ZONE 1, and the rear unit ZONE 2 configuration should have Dip switch 5 (ZONE will be ZONE 2.
  • Page 76 Section D - Configuration, cont’d. FIG. D39 Two Basement Heat Pumps Plus One Gas Furnace ZONE 1 configuration should have all Dip switches to To configure two basement heat pumps plus one gas fur- OFF position. The ambient sensor should be plugged nace, ZONES need to be established.
  • Page 77 Section D - Configuration, cont’d. FIG. D40 FIG. D41 FIG. D42...
  • Page 78 Section D - Configuration, cont’d. The two (2) furnace thermostat wires from rear furnace Two Rooftop Air Conditioners Plus Two Gas Furnaces To configure two rooftop air conditioners plus two gas fur- are to Zone 2 (rear) air conditioner. naces, ZONES need to be established. For explanation ZONE 1 configuration should have all Dip switches to purposes, the front air conditioner and one furnace will be OFF position and the cold (freeze) control plugged into...
  • Page 79 Section D - Configuration, cont’d. FIG. D45 FIG. D46...
  • Page 80 Section D - Configuration, cont’d. One Rooftop Heat Pump Plus One Rooftop Air Conditioner ZONE 2 (air conditioner) configuration should have Dip switch 5 (ZONE 2) to ON position and all other Dip Plus Two Gas Furnaces switches to OFF position. The cold (freeze) control To configure one rooftop heat pump plus one rooftop air conditioner plus two gas furnaces, ZONES need to be es- should be plugged into P5 (blue) connector.
  • Page 81 Section D - Configuration, cont’d. FIG. D50 4. Four Comfort Zones 3. Three Comfort Zones To configure three units, ZONES need to be established. To configure three units, ZONES need to be established. Refer to Section 2.3A and 2.3B for Zone 1 and Zone 2 Refer to Section 2.3A, 2.3B and 2.3C for Zone 1, Zone 2 and Zone 3 configuration.
  • Page 82 DUO-THERM ROOF MOUNTED HEAT PUMPS This program will address the most common system problems associated with the Duo-Therm Heat Pumps supplied by The Dometic Corporation. Our intent is to provide you with a guideline of checks to make, should you encounter one of the following symptoms.
  • Page 83 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE 2.Fan operated; compressor will not come on (does not “hum). (Cool or Heat Mode) Mechanical Controls Wiring A3, C21 1, 58 Selector Switch Mechanical Thermostat...
  • Page 84 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan Operates; compressor tries to start, cycles “OFF” and hums again, or blows circuit breaker (Cool or Heat Mode)... Cont’d Bimetal Controls AC Voltage...
  • Page 85 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan operates; compressor runs for a short while, cycles off, cycles back on hums, blows circuit breaker or does not run. (Cool or Heat Mode)
  • Page 86 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE 5. Compressor runs, no fan (Cool or Heat Mode) Mechanical Controls Wiring Selector Switch Fan/Run Capacitor Motor Bimetal Control System Wiring Fan/Run Capacitor Motor...
  • Page 87 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Compressor runs, fan runs, but on one speed only. (Cool or Heat Mode) Analog Control System Wiring Fan/Run Capacitor Motor Cable Assembly Analog Thermostat...
  • Page 88 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Inside Coil Freezes up (Air Distribution Box) (Cool Mode)...cont’d Comfort Control Center System Ambient Temperature C22a Air Flow Obstruction C22j Thermostat Location Low Refrigerant Charge...
  • Page 89 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Inside Coil Freezes up (Duct in Ceiling) (Cool Mode) Comfort Control Center System Ambient Temperature C22a Ducting System Air Flow Obstruction C22j Heat Gain/Heat Loss...
  • Page 90 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Insufficient cooling or heating compressor runs constantly... (Ducts in ceiling) Analog Control System Air Flow Obstruction C22j Ducting System Heat Gain/Heat Loss C22b Sealed System...
  • Page 91 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE 12. Insufficient cooling or heating; compressor cycles off and on...(Air Distribution Box) Mechanical Controls ADB Installation Operation Heat Gain/Heat Loss C22b Air flow Obstruction...
  • Page 92 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Insufficient cooling or heating; compressor cycles off and on...(Duct in Ceiling)...cont’d Comfort Control Center System Operation Short Cycle C22i Ducting System Heat Gain/Heat Loss...
  • Page 93 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Excessive cooling or heating; compressor will not shut off...cont’d Analog Control System Thermostat Location Analog Thermostat C18c Cable Assembly Relay Analog Control Box C17d...
  • Page 94 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Water leaks into RV. (Cooling Mode)...cont’d Analog Control System Installation C22f Drain Pan C22g Roof Gasket Comfort Control Center System Installation C22f Drain Pan...
  • Page 95 DUO-THERM BASEMENT HEAT PUMPS This program will address the most common system problems associated with the Duo-Therm Heat Pumps supplied by The Dometic Corporation. Our intent is to provide you with a guideline of checks to make, should you encounter one of the following symptoms.
  • Page 96 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan operates; compressor will not come on (does not “hum”)... Cont’d. Analog Control System Operation Overload protector Compressor Fuse Breaker Analog Thermostat C18d Analog Control Box...
  • Page 97 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan operates; compressor will not come on (does not “hum”). Bimetal Control System Operation Wiring A3, C21 1, 58 Changeover Thermostat Cable Assembly Bimetal Thermostat...
  • Page 98 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan Operates; compressor tries to start, cycles “OFF” and hums again, or blows circuit breaker. Comfort Control Center System AC Voltage PTCR or Start Relay...
  • Page 99 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE 5.Compressor runs, no fan Bimetal Control System Wiring Fan/Run Capacitor Motor Bimetal Thermostat C18b Cable Assembly Relay Printed Circuit Board C17a Analog Control System Wiring...
  • Page 100 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE 7.Inside Coil Freezes up Bimetal Control System Ambient Temperature C22a Ducting System Air Flow Obstruction C22j Heat Gain/Heat Loss C22b Thermostat Location Cable Assembly Fan/Run Capacitor...
  • Page 101 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE 8. Insufficient cooling or heating compressor runs constantly... Bimetal Control System Ducting System Heat Gain/Heat Loss C22b Sealed System Compressor Analog Control System Ducting System...
  • Page 102 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE 10. Insufficient cooling or heating; compressor cycles off and on... Bimetal Control System Operation Short Cycle C22i Ducting System Heat Gain/Heat Loss C22b Air flow Obstruction...
  • Page 103 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT HEAT PUMPS...Continued SYMPTOMS CAUSE REFER TO PAGE 12. Noisy operation. (Cool or Heat Mode) Bimetal Control System Loose parts C22c Fan Blade C22e Tubing Vibration C22d Reversing Valve Analog Control System Loose parts...
  • Page 104 DUO-THERM ROOF MOUNTED AIR CONDITIONERS This program will address the most common system problems associated with the Duo-Therm Heat Pumps supplied by The Dometic Corporation. Our intent is to provide you with a guideline of checks to make, should you encounter one of the following symptoms.
  • Page 105 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE 2. Fan operates; compressor will not come on (does not “hum”). Mechanical Controls Wiring A3, C21 1, 58 Selector Switch Mechanical Thermostat C18a Overload...
  • Page 106 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan Operates; compressor tries to start, cycles “OFF” and hums again, or blows circuit breaker (Cool or Heat Mode)... Cont’d Bimetal Controls AC Voltage...
  • Page 107 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan Operates; compressor tries to start, cycles “OFF” and hums again, or blows circuit breaker... Cont’d Bimetal Controls AC Voltage PTCR or Start Relay...
  • Page 108 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan operates; compressor runs for a short while, cycles off, cycles back on hums, blows circuit breaker or does not run. (Cool or Heat Mode)
  • Page 109 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE 5. Compressor runs, no fan Mechanical Controls Wiring Selector Switch Fan/Run Capacitor Motor Bimetal Control System Wiring Fan/Run Capacitor Motor Bimetal Thermostat C18b Cable Assembly...
  • Page 110 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Compressor runs, fan runs, but on one speed only...cont’d Analog Control System Wiring Fan/Run Capacitor Motor Cable Assembly Analog Thermostat C18b Relay Analog Control Box...
  • Page 111 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Inside Coil Freezes up (Air Distribution Box)...cont’d Comfort Control Center System Ambient Temperature C22a Air Flow Obstruction C22j Thermostat Location Low Refrigerant Charge C20c...
  • Page 112 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Inside Coil Freezes up (Duct in Ceiling)...cont’d Comfort Control Center System Ambient Temperature C22a Ducting System Air Flow Obstruction C22j Cold Control Heat Gain/Heat Loss...
  • Page 113 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Insufficient cooling or heating compressor runs constantly. (Ducts in ceiling)...cont’d Analog Control System Air Flow Obstruction C22j Ducting System Heat Gain/Heat Loss C22b Sealed System...
  • Page 114 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE 12. Insufficient cooling or heating; compressor cycles off and on...(Air Distribution Box) Mechanical Controls ADB Installation Operation Heat Gain/Heat Loss C22b Air flow Obstruction...
  • Page 115 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Insufficient cooling or heating; compressor cycles off and on...(Duct in Ceiling)...cont’d Comfort Control Center System Operation Short Cycle C22i Ducting System Heat Gain/Heat Loss...
  • Page 116 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Water leaks into RV...cont’d Analog Control System Installation C22f Drain Pan C22g Roof Gasket Comfort Control Center System Installation C22f Drain Pan C22g Roof Gasket 16.
  • Page 117 Section E - Symptom/Cause Chart, cont’d. DUO-THERM ROOF MOUNTED AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Turn to electric heat strip; no operation...cont’d Comfort Control Center System Configuration Operation Wiring A3, C21 1, 58 Cable Assembly Comfort Control Center C18d...
  • Page 118 DUO-THERM BASEMENT AIR CONDITIONERS This program will address the most common system problems associated with the Duo-Therm Heat Pumps supplied by The Dometic Corporation. Our intent is to provide you with a guideline of checks to make, should you encounter one of the following symptoms.
  • Page 119 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan operates; compressor will not come on (does not “hum”)... Cont’d. Analog Control System Operation Overload protector Compressor Fuse Breaker Analog Thermostat C18d Analog Control Box...
  • Page 120 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan operates; compressor will not come on (does not “hum”). Bimetal Control System Operation Wiring A3, C21 1, 58 Changeover Thermostat Cable Assembly Bimetal Thermostat...
  • Page 121 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Fan Operates; compressor tries to start, cycles “OFF” and hums again, or blows circuit breaker. Comfort Control Center System AC Voltage PTCR or Start Relay...
  • Page 122 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE 5.Compressor runs, no fan Bimetal Control System Wiring Fan/Run Capacitor Motor Bimetal Thermostat C18b Cable Assembly Relay Printed Circuit Board C17a Analog Control System Wiring...
  • Page 123 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Compressor runs, fan runs, but on one speed only...cont’d Comfort Control Center System Wiring Fan/Run Capacitor Motor Cable Assembly Comfort Control Center C18d AC Power Module Board C17c 7.
  • Page 124 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE 8.Insufficient cooling or heating compressor runs constantly... Bimetal Control System Ducting System Heat Gain/Heat Loss C22b Sealed System Compressor Analog Control System Ducting System Heat Gain/Heat Loss...
  • Page 125 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE Insufficient cooling or heating; compressor cycles off and on...cont’d Analog Control System Operation Short Cycle C22i Ducting System Heat Gain/Heat Loss C22b Air flow Obstruction...
  • Page 126 Section E - Symptom/Cause Chart, cont’d. DUO-THERM BASEMENT AIR CONDITIONERS...Continued SYMPTOMS CAUSE REFER TO PAGE 12. Noisy operation. Mechanical Controls Loose parts C22c Fan Blade C22e Tubing Vibration C22d Bimetal Control System Loose parts C22c Fan Blade C22e Tubing Vibration...
  • Page 127 This Manual is Compliments of Northwest RV Supply 86325 College View Road Eugene, OR 97405 Local: 541-746-9092 Toll-Free: 866-678-7467 Fax: 541-736-5573 http://www.nwrvsupply.com mail@nwrvsupply.com Northwest RV Supply carries a large spectrum of surplus, used, and new RV parts and components. Please feel free to visit our website for additional information.

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