atwood furnace question

Discussion in 'General RVing' started by havns3, Dec 9, 2004.

  1. havns3

    havns3 New Member

    I have a 1988 prowler regal fifth wheel. It has two ducted hydroflame 8520 series II furnaces in it. The one in the rear works fine but the one in the front will fire when on first cycle most of the time and run until thermostat shuts it off. But when it is started again it will fire and run for about 20 seconds give or take a couple of seconds and the burner will shut off but the fan will continue to run. if I turn the thermostat off and wait a hour or two and try it again it will work but then it does the same thing. I can see a daubers nest in the burner area but I am not for sure how to get to it to clean it out I am mechanically inclined but just never took one of these apart.

    CAn anyone help me with diagnoises. I think it could be the limiting switch. Does anyone have a technical service manual for this model furnace?

    thanks,
    charles
     
  2. Poppa

    Poppa Member

    atwood furnace question

    Charles,
    As to how to remove the dirt duabers nest, try a piece of plastic hose taped to the end of a vacuum cleaner. The hose will mormally break up the nest and the cleaner will suck up the residue.

    As to the unit coming on and not staying lit, it sounds like a thermocouple problem. This will be a small tube about as round as a small pencil and 2 inches long. This tube should be in the area of the flame. It sends a signal back to a unitrol valve that senses a flame. If it does not sense a flame it will not allow the gas to come on. This is a safety device. As to the blower staying on for a while after the flame goes out, this is a sensor that is in the duct and its purpose is to crculate air until the heat is reduced to a low level in the plenum chamber.

    This is about all I can say without additional information.

    If the dirt daubers nest is covering the thermocouple, cleaning it out may solve your problem.
     
  3. Kirk

    Kirk Senior Member

    atwood furnace question

    Why it works the first time, I don't know, but your symptom is the classic one for mud dobber nests. For some reason that nest isn't restricting the air flow enough to prevent ignition untill after the furnace has run for a while. But any opstruction in the air path for combustion will reduce air flow and that in turn will cause the sail switch to fail to close. The sail switch is in series with the solenoid of the gas valve and if it fails to open, you get exactly what you have. Any RV repairman can tell you that mud dobbers are the #1 cause of that problem, but it usually doesn't light the first time. The suggested method of removal sounds to me like a good one. You can access the burner by opening the access pannel after loosening the two screws at the top corners of the pannel. If yo look into the lower right corner, above and to the left of the exhaust outlet, there is a wing nut there that you can remove to pull the cover off of the exhaust area in order to access it. I would use the hose and vacume method to remove it. Once you have done so, test your furnace again because there is a very high probability that you will have no more problems.

    Once you have it running properly, I strongly suggest that you buy one of the stainless steel screens made to keep bugs out of the furnace, for each of your furnaces. They cost a bit, but they wont rust and inhibit air flow like window screen would and they will prevent that ever happening again.
     
  4. Kirk

    Kirk Senior Member

    atwood furnace question

    Isn't that a neat way to spell obstruction?

    And by the way, I have the same furnace and I assure you that you don't have any thermal couples in your furnaces.
     
  5. havns3

    havns3 New Member

    atwood furnace question

    thanks for the advice i will try it and let you know how it works out thanks again
     

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