Truck Camper Furnace is Running However there is NO HEAT !

You may find yourself in such a situation some cold morning.  Explanation of the components and operation of a typical TC furnace may help you to find the culprit.

Starting with the thermostat – ensure the temperature setting is above the current temperature of the truck camper. 

Furnace Access Panel
Furnace Access Panel

If you are on shore power confirm you have power by ensuring there is a display on your microwave. 

Next, open the furnace access panel.   Locate the control board and ensure there is a lite green power light on the control board.  This indicates the presence of 12 volts. 

Dinosaur Electronics Universal Ignitor Board with Fan Control

 

 

 

 

 

 

Atwood Sail Switch
Atwood Limit Switch

The fan should run for 15 to 20 seconds to purge the combustion chamber of any remaining gas fumes.  If you hear a clicking sound this indicates that the control board is trying to open the gas solenoid valve and you may smell propane.  If this is the case,  there is a high possibility that the control board, the sail switch, or the high limit switch are not the cause of your problem.

On the control board is also a red error light with only four possible faults indicator to help you diagnose a problem:

  • Steady red light = internal control board failure
  • 1 (One) flashing red light with a 3-second pause = high limit switch or sail switch failure
  • 2 (Two) flashing red light with a 3-second pause = flame sense fault
  • 3 (Three) flashing red lights with a 3-second pause = ignition lockout fault

The flashing red light comes with a three-second pause that is fairly straightforward and should help you count the number of flashes.

Explanation time – from the control board, 12-volts goes to the sail switch (this switch senses if the electrical power is too low to run the fan at the correct speed to support combustion) and then to the high-temperature limit switch (the limit switch is a normally closed switch and is designed to “snap-open” when the furnace experience an over-temperature condition) then on to opening the gas solenoid valve.  At this point, if you hear a clicking sound and smell propane the problem most likely is in the combustion chamber. 

Next, inspect the components that make up the combustion chamber. 

Turn off the propane.  Remove the furnace exhaust pipe.  Depending upon the bass fitting connection, you may need TWO wrenches to disconnect the gas line from the gas valve. Disconnect the two electrical wires that feed the valve.  One wire is the power to the gas solenoid  (AKA gas valve) and the other is ground.  The thick black wire is for the electrode and can be disconnected at the control board.

TIP – When reinstalling the gas solenoid, connect the gas line fitting a couple of turns before securing the burner screen unit.

Next, the gas solenoid, the burner, and electrode (secured by three screws) can be removed as one unit by pulling the unit out towards you.

Burner Compatible with Atwood furnace

Check the serviceable condition of the burner screen for rips or torn areas and is free from carbon build-up. There should be a 1/8” separation between the burner and the electrode. Plus a  1/8” separation between the positive and negative posts of the electrode.  If either clearance is incorrect, carefully bend the electrode post(s) to obtain the 1/8″ clearance.

TIP – When reinstalling the gas solenoid, connect the gas line fitting a couple of turns before securing the burner screen unit.

Atwood Electrode Assy

 

Replace all questionable parts as you seem fit. 

Keep in mind that when ordering replacement parts that you need the part number of your furnace to ensure proper part replacement.



Note:  The parts shown above may not match your furnace 100% – original parts and any replacement parts may differ in appearance.  However, the description of the furnace’s operation and the related parts are very similar to those in your furnace.