Forum Discussion

_camperprobs's avatar
_camperprobs
Explorer
Sep 30, 2017

Duo Therm forced air furnace wont ignite

Hi everyone!


New to this forum and truck camperin' in general (not off to the best start lol)! I have an old 1979 Vangaurd truck camper and one of the( many) issues I am having is that the pilot light in my furnace is working however it wont engage fully and the fan will not spin. I have taken the unit out of the camper and "bench tested" it by checking that there was power going to each wire, and there was, however with the pilot on it wont turn on! I figure that even if the fan doesn't move, at least the unit would ignite normally? only thing I can think of is something messed up with the TH/TR connection. Can I touch the two wires together to bypass the connection to test this safely?

Thanks!

Truck Campers

10 Replies

  • _camperprobs's avatar
    _camperprobs
    Explorer
    Oct 02, 2017
    tattoobob wrote:
    If it's a standing pilot it should light even if the fan isn't running, if it's electronic ignition the fan should start then you should hear a clicking sound that's the pilot trying to start the burner

    So if you have a standing pilot change the Thermocouple

    If electronic check the fan or any safety switches could be a reset or bad switch also check the fan motor


    I think your definitely right about it being the fan motor. Unfortunately this camper and heater model is so old that there’s no way I’m going to find a new fan haha. I’ll just pay the $400 and get a decent new unit and my old camper will be good for another many years!

    Thanks for all the suggestions and help everyone
  • tattoobob's avatar
    tattoobob
    Explorer
    Oct 01, 2017
    If it's a standing pilot it should light even if the fan isn't running, if it's electronic ignition the fan should start then you should hear a clicking sound that's the pilot trying to start the burner

    So if you have a standing pilot change the Thermocouple

    If electronic check the fan or any safety switches could be a reset or bad switch also check the fan motor
  • 1mtnman's avatar
    1mtnman
    Explorer II
    Oct 01, 2017
    Google your type of furnace for a youtube demonstration. I'm sure you will find a video describing your problem. If you have to replace the sail fan go to Amazon and they are less than $20.00 and very easy to install. I would say if the fan is not running at all it is probably something other than the sail fan.
  • _camperprobs's avatar
    _camperprobs
    Explorer
    Oct 01, 2017
    work2much wrote:
    While it's on the bench put 12 volts right across the fan and see if it will run. Many units same motor runs both interior and exterior fans on same spindle. Do the fans spin by hand?


    Fan spins easily by hand. I have a red wire and a black wire that goes to the TH (or TR) terminal. Should it fire up if I just put the red wire directly to the positive on the battery?
  • work2much's avatar
    work2much
    Explorer
    Sep 30, 2017
    While it's on the bench put 12 volts right across the fan and see if it will run. Many units same motor runs both interior and exterior fans on same spindle. Do the fans spin by hand?
  • _camperprobs's avatar
    _camperprobs
    Explorer
    Sep 30, 2017
    work2much wrote:
    darsben1 wrote:
    THERE is usually a sail switch that stops the main burner from igniting unless the fan is turning


    Yes, this. No fan running, no burner ignition. First step is to repair fan. While you are in there you can test the sail switch for connectivity while in the on position.



    I'm guessing a defective fan as well! I pushed the sail switch to the on position and still nothing happened. I connected the thermostat wires together to make sure I had a solid connection but I am just not able to get anything.

    Anyway to bypass the sail switch so that I can at least see the pilot ignite? Do you think this old unit has some feature where if fan doesn't work then it won't allow the unit to ignite?

    Thanks for all your help.
  • work2much's avatar
    work2much
    Explorer
    Sep 30, 2017
    darsben1 wrote:
    THERE is usually a sail switch that stops the main burner from igniting unless the fan is turning


    Yes, this. No fan running, no burner ignition. First step is to repair fan. While you are in there you can test the sail switch for connectivity while in the on position.
  • midnightsadie's avatar
    midnightsadie
    Explorer II
    Sep 30, 2017
    I think your fan should run about 30 seconds or longer to blow out the system then it starts the furnce ,might google your problem.
  • darsben1's avatar
    darsben1
    Explorer
    Sep 30, 2017
    THERE is usually a sail switch that stops the main burner from igniting unless the fan is turning

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