Furnace blows cold air only

Discussion in 'Talkback' started by melreck, Mar 27, 2006.

  1. melreck

    melreck New Member

    Motorhome is a 1993 Coronado, Furnace is the normal therostat controlled Suburban forced air unit. It was working fine last time I used it. Getting ready for a trip and checking all things out, furnace came on as usual, but did not ever light and blow heat. I am suspicious it is the igniter. Are they difficult to replace? Any help in how to test and replace will be appreciated. Thank you in advance. Mel
     
  2. hertig

    hertig Senior Member

    Furnace blows cold air only

    First step is to check for critters in the burner area. Insects love to build nests in there, which prevent it from working
     
  3. melreck

    melreck New Member

    Furnace blows cold air only

    Hertig, Thanks for the suggestion, but no critters. I removed the furnace and took it to Kampers Korner in Victorville. Worth the $40 dollar charge and the 50 mile drive. They put it on the bench and hooked up propane and power and it fired right up. One of two things can be the problem, lack of propane, not likely, or a bad thermostat. I had check for power at the contact points and it was live. I did not check for power at the other end of the wires where they plug into the unit. I will do that as soon as I can and will post the results. Thanks for your help. Mel :)
     
  4. Kirk

    Kirk Senior Member

    Furnace blows cold air only

    I suggest that you check some other things. By far the most common cause of the symptom that you have is the sail switch. It is a safety switch that is actuated by the air movement inside of the furnace if the blower is moving enough air for safe combustion. There are many things that can cause it not to close and if it doesn't the gas valve will never open and you get air blowing, and nothing more. If you were operating on the battery that is the first thing to check. You need to have at least 11V at the blower motor for it to be sure and turn fast enough to close the sail switch. Another common cause of it not closing is a collection of wasp, spider and mud-dauber nests in the flue area because that will restrict combustion air movement. You can check for a sail switch problem by checking with a meter to see if there is 12V at the gas valve. It there is, the sail switch is closed.
     
  5. melreck

    melreck New Member

    Furnace blows cold air only

    Took the furnace to the shop and they hooked it up on the bench and it worked fine. Took it home, put it back in the MH and blower comes on, no heat. Could it be something with my battery disconnect? Mel
     
  6. Kirk

    Kirk Senior Member

    Furnace blows cold air only

    That sure sounds like low voltage. Have you checked the voltage at the motor?
     
  7. melreck

    melreck New Member

    Furnace blows cold air only

    Thanks Kirk, I think the voltage must be low as taking it off shore power and starting the generator up, I had heat. Went back to shore power and no heat again. My shore power comes from a 100 foot long cable. It has had the insulation broken in a couple of places. Tomorrow I am going to try a different cable and I will let you know if that works ok. Thanks, Mel
     

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