Pilot Model RV FurnaceOperationElectrically, the Furnace basically consists of a Fan Circuit and a Gas Circuit. Both circuits are controlled by the Thermostat.
WARNINGWhile the information here is for general reference, using it is at your own risk.
If you do not feel comfortable with working on Propane Gas appliances,
then enlist the services of a qualified technician.
WARNINGPurging of all Propane Gas from the Pilot Model RV Furnace Combustion Chamber for 5 minutes prior to lighting/re-lighting the Pilot Light is extremly important.
This prevents a build of gas that could result in an explosion.
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WARNINGOver time the combustion chamber rusts through allowing Gas fumes to enter the interior of the RV.
You will need to replace the furnace if this occurs.
CAUTIONWhile the simplified drawings posted here help in describing how a furnace works,
always refer to the actual unit drawing when evaluating or working on a RV Furnace.
Components (i.e. extra Limit Switches, etc.) may be installed that are not represented here.
Typically, the elctrical schematic for the furnace can be found glued to the inside of the Furnace.



Referring to the drawing above:
- +12VDC power (+10.5VDC to +13.5VDC) is applied to the circuit breaker or fuse if so equipped.
- The +12VDC is then feed through the Unit Power ON/OFF switch and distributed to the Thermostat, Fan Switch and the input side contact of the Fan Relay.
The Fan Switch is a thermo switch and is normally open. The Fan Switch closes when the furnace heats up. - When the Thermostat requests heat (contacts close), +12VDC is feed to the Fan Relay (Fan Circuit) and the Sail Switch (Gas Circuit).
- The Fan Relay energizies and applies power to the Fan Motor. On some models, a starting capacitor is installed that assists the Fan Motor start. DC Voltage for the fan returns to the battery via the +12VDC return path.
- The sail switch is normally open. When the fan reaches to 75% of it's rated capacity, the Sail Switch closes routing +12VDC voltage to the Thermal Limit Switch.
- The Thermo Limit switch is normally closed and passes the +12VDC power on to the Gas Valve. The Limit switch will open shutting power to the Gas Valve if the furnace internal temperature goes to high.
- The Gas Valve is a electricly operated solinoid valve, provides gas to the main burner, provides gas to the Pilot Light, and senses the status of the Pilot Light. Sensing of the Pilot Light is performed electrically via a voltage induced in the Thermocouple by the Pilot Light. If the Gas Valve does not sense the Pilot Light signal it will not provide gas to the main burner.
- When the Thermostat senses the desired temperature in the room has been achieved, it opens the contacts shutting off voltage to the Fan Relay and Gas Valve circuits. The Fan Switch will keep providing +12VDC supply voltage to the Fan Motor until the temperature inside the Furnace is reduced at which point the switch opens securing power to the Fan Motor.
- Glow Coil Models - When the Pilot Light switch is depressed, the Thermostat and fan circuits are disabled.
- DuoTherm Models - Even though the Thermostat is located on the return leg side of the circuit, it essentially controls both the Fan and Gas valve circuits the same way.
CAUTIONJust as the motor on a vacuum cleaner will increase speed if you place your hand over the intake hose,
the RV Furnace fan motor will increase speed if the inside air intake ports are blocked by camping supplies, linen, cookie sheets, etc.
This can result in a increase in combustion air flow that causes the furnace to run hotter.
The overheating can cause damage to the furnace unit. Do not block the furnace air intake and exhaust ports.
Notes:1. If the Thermostat applies +12VDC voltage to the Fan Relay and the Gas circuit does not operate (i.e Pilot Light is not lit), the Fan Motor will keep running until either the Thermostat is turned OFF or the input supply voltage is drained.
2. If the propane supply runs out and the Thermostat is on, the Fan Motor will keep running until either the Thermostat is turned OFF or the input supply voltage drained.
3. If either the Combustion side Air Intake/Exhaust path (i.e. birds/wasp nest) or the Room side Air Intake/Exhaust path (i.e. camping gear) is blocked, the fan will typically not get up to 75% capacity. This will prevent the Sail Switch from closing and allowing voltage to get to the gas valve.
4. Overtime the combustion chamber rusts through. You will need to replace the furnace if this occurs.
5. If the propane system in the RV has been purged, then it is best to purge most of the air out of the system using the burners on the stove prior to attempting to light the furnace. Even so, it my still take multiple attempts to start the furnace in order to purge the air from the furnace gas lines.
6. When turning the Propane system on at the tank, turn the gas on very slowly. There is a safety valve in the propane tank that is used to drastically reduce the flow from the tank to the regulator if it senses a large volumn of propane is discharged from the tank. This is safety feature where if the RV is in an accident and the propane lines are ruptured, the gas flow is greatly reduced. If the safety valve is triggered, to reset it, you have to turn the tank supply OFF for 60 seconds and then very slowly open the tank supply valve.
7. Even though Propane suppliers strive not to get moisture in their delivery systems, a small amount of moisture does get in. On very cold days, this moisture can then freeze in your regulator stopping the flow of gas into the RV. You have to warm up (no flames!; warm towel, etc.) the regulator to get it working again.
TroubleshootingBURNER FAILS TO IGNITE AND BLOWER FAILS TO RUN Condition
| Solution
|
1. No electrical power to the furnace; current overload protector device defective or, tripped (circuit breaker)
| Reconnect or replace power source Reset circuit breaker Check amp draw from motor according to furnace's specification.
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2. Thermostat defective
| Replace thermostat
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3. Thermostat wires broken
| Replace wire or wires Relocate thermostat
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4. Blower motor defective
| Replace motor
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5. Wire off Blower motor
| Reconnect wire
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6. Blower relay defective
| Replace relay
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7. Wire off relay
| Reconnect wire
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8. Improper ground
| Clean and secure grounds
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BLOWER RUNS BUT FURNACE FAILS TO IGNITE Condition
| Solution
|
1. Low voltage (less than +10.5VDC)
| Correct Power Supply
|
2. 12 volt polarity reversed
| Correct polarity
|
3. Furnace grounding wires not secure
| Clean and secure grounds established
|
4. Gas valve defective
| Replace valve or valve coil, depending on problem encountered
|
5. Gas pressure incorrect
| Set pressure to a minimum of 11"W.C. with all appliances running (Replace regulator if not obtainable)
|
6. Limit switch defective or wire off
| Reconnect wire or replace Limit Switch
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7. Sail switch defective or wire off
| Reconnect wire or replace Sail Switch
|
8. Burner orifice defective
| Clean main burner orifice or replace.
|
9. Combustion air wheel loose
| Reposition and tighten
|
10. Burner head adjustment
| Reposition and tighten Adjust burner according to furnace specifications.
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11. Exhaust blocked
| Clean exhaust
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12. Air intake restricted
| Clean air intake
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13. Broken or loose wire
| Replace or tighten
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14. Motor running slow
| Check voltage first (greater than +10.5VDC) If 12 VDC while running, replace motor
|
BLOWER SHUTS OFF AT SAME TIME BURNER SHUTS OFF Condition
| Solution
|
1. Faulty Fan Switch or Fan Relay
| Replace Fan Switch or Fan Relay
|
2. Thermostat wired wrong
| Correct wiring
|
BURNER CYCLING ON AND OFF - BLOWER RUNS CONTINUOUSLY WITH THERMOSTAT "ON" Condition
| Solution
|
1. Restricted return air supply
| Make sure return air meets furnace's minimum requirements.
|
2. Restricted discharge duct system
| a. Make sure ducting meets furnace's minimum requirements b. Make sure there is no excess ducting or unnecessary bends c. Make sure any closeable registers are fully open and unrestricted
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3. Defective limit switch
| Replace limit switch.
|
4. Furnace over fired
| Set gas pressure to a minimum of 11"W.C. with all appliances running. Replace regulator if not obtainable Also, check main burner orifice, it must comply with furnace's specifications.
|
BLOWER VIBRATES OR IS NOISY Condition
| Solution
|
1. Damaged blower wheel
| Replace blower wheel.
|
2. Motor shaft bent
| Replace Fan Motor.
|
3. Loose motor
| Tighten motor mounting bracket.
|
4. Restricted discharge duct system
| a. Make sure ducting meets furnace's minimum requirements b. Make sure there is no excess ducting or unnecessary bends c. Make sure any closeable registers are fully open and unrestricted
|
PILOT FAILS TO IGNITE OR STAY LIT Condition
| Solution
|
1. Plugged pilot orifice
| Clean or replace orifice.
|
2. Electrode out of adjustment (Glow coil or Piezo sparker equipped furnace)
| Adjust electrode to furnace's specifications.
|
3. Pilot tube defective
| Replace tube.
|
4. Piezo sparker defective
| Replace sparker.
|
5. Defective thermocouple
| Replace thermocouple.
|
6. Defective valve
| Replace valve.
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7. Vent kit not sealed
| Seal vent where it meets the furnace.
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8. MICA window missing
| Replace MICA window.
|
9. Combustion air hose plugged or collapsed
| Replace combustion hose.
|
10. Burner plate gasket or pilot not sealed
| Replace gaskets.
|
11. Water in propane
| Add alcohol to the propane bottles.
|
LAZY FLAME (Yellow) Condition
| Solution
|
1. High gas pressure
| Set pressure to a minimum of 11"W.C. with all appliances running. Replace regulator if not obtainable
|
2. Burner out of adjustment
| Adjust burner according to furnace specification
|
3. Combustion wheel installed backwards
| Reposition wheel and tighten.
|
4. Air leakeage at gaskets
| Replace gaskets.
|
5. Low voltage (less than +10.5VDC)
| Correct power supply.
|
FAN RUNS CONTINOUSLY WITH THERMOSTAT "OFF" Condition
| Solution
|
1. Defective thermostat
| Replace thermostat.
|
2. Shorted thermostat leads
| Replace/repair wire or wires.
|
3. Defective Fan Switch
| Replace Fan Switch.
|
4. Defective Relay
| Replace Relay.
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INSUFFICIENT HEAT Condition
| Solution
|
1. Defective thermostat
| Replace thermostat.
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2. Furnace under fired
| 1. Set gas pressure to 11"W.C. with all appliances running. Also, check main burner orifice, it must comply with furnace's specifications 2. Check ducting and return air according to furnace's specifications.
|