Atwood furnace cycles on & off

Discussion in 'Heating / Cooling Systems' started by timo4352, Oct 19, 2013.

  1. timo4352

    timo4352 New Member

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    Hello everyone. My name is Tim and I've just got my first popup. I'm just checking things out too make sure I know how to set up and everything works before we head out in a trip. I do have one question that I haven't yet been able to find an answer to and I'm sure someone here will know or have had a similar experience.
    The camper has an Atwood furnace. I think it is a 7912-II. I'm running the camper on 110 volts right now. The furnace fired up fine after a couple times and I can feel heat coming out - that's the good part. But then it starts to cycle - I can hear the burner shut off and the fan still running for 8 to 10 seconds. Then the burner kicks in again - for about 8 to 10 seconds. Then the process repeats. I can feel a temperature difference and hear the burner so I know it's shutting down the burner - but why? I hope it's something simple and not an expensive fix. I do not know the fullness of the propane tank. Regulator maybe? I can't imagine that this is the way it is designed to work - it would keep me awake at night. Doesn't it work more like one's house furnace?
    I should mention the pup is a '97 Palomino Yearling.
    Thanks in advance for your answers.
    Tim
     
  2. Wizfisher

    Wizfisher New Member

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    It's supposed to shut off the heat once the desired temp is reached.
    The fan will continue to blow out any heat that is in the furnace.
    (Same as a fan on an a/c will blow out remaining cold air)

    Once it gets colder again, the furnace will kick on again repeating the process.


    You can change your t-stat to a digital and regulate the cycles a little better.

    Reading your post again, it sounds as if the fan is not turning off and the burner is coming on again? Might be a t-stat issue.
     
  3. tombiasi

    tombiasi Well-Known Member

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    Check to see that the hot air is not blowing on your thermostat.
     
  4. tconroy

    tconroy Active Member

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    do you have the door or windows open? I would check the thermostat wire going into the back or turn the thermo stat up and see what happens they are senitive and on mine it is right by the door which is kinda silly if you ask me. If I open the door the furnace comes on when the air rushes in.
     
  5. timo4352

    timo4352 New Member

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    Well, I did find that one of the side vent covers was off - found it on the floor in the cabinet. Mine is set up to just discharge from the front only. So I put that cover back on. I also pulled the outside exhaust vent and looked in there for bugs or mice or whatever. It was perfectly clean so that got buttoned back up. I cranked up the heat anticipater to try to lengthen the cycle, but I'm not yet sure if that helped. I'm thinking it maybe all in the thermostat because if I crank it all the way upo to 90 it will continue to run. Set at 75 it won't. I know it's not 75 degrees in there though.
    I could just try a new stat, but I hate to buy stuff I don't need and still have the same problem, ya know?
    The fan continues to run and the burner cycles on and off when set at a lower temp - say 75.
    I keep hearing digital stat mentioned - that's the best one to get, huh?
    Thanks again
    Tim
     
  6. rabird

    rabird Howdy!

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    I would take the cover off the thermostat and watch it as it 'cycles' at 75.
    Do the contact come apart and then go back quickly?

    You can bypass the thermo by disconnecting and connecting the two wires together as a test.

    It is weird that it has different operation at different thermo setting!

    from http://bryantrv.com/docs2/docs/hflamefurn04.pdf
    LIMITING = BURNER CYCLING ON AND OFF - BLOWER RUNS CONSTANTLY WITH THERMOSTAT ON
    Restricted or insufficient discharge ducting ------------a. Ducting must meet furnace’s minimum requirements.*
    b. No excess ducting or unnecessary bends.*
    c. All closeable registers must be fully open and unrestricted.*
    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.*
    Restricted return air supply ----------------------------------Make sure return air meets furnace minimum requirements.*
    Defective limit switch ------------------------------------------Replace limit switch
     
  7. Unstable_Tripod

    Unstable_Tripod Well, there's your problem!

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    Without a lot of heat retention measures (Gizmos, Reflectix, etc.) maintaining 75 in a PUP is pretty unlikely. Most folks shoot for 55 or 60.
     
  8. xshield

    xshield New Member

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    x2.
     
  9. timo4352

    timo4352 New Member

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    I agree !00% - and I'm just a beginner here. The temp inside was probably closer to 55-60. At 75 I would've been sweating. I know the thermostat has to be off. I'm gonna try bypassing the thermostat tomorrow and see what happens. Any recommendation for a decent replacement thermostat?
     
  10. RangerZ

    RangerZ Member

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    Re: Atwood furnace cycles on & off

    Maybe check to be sure propane is connected and flowing well? When I had a bad connection in a storm one night my furnace was acting up like you describe. Just disconnect and reconnect, or try a different tank? Might be worth it to check before you replace the thermostat....
     
  11. timo4352

    timo4352 New Member

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    Thanks for the reply. I'll try that too. I did check and the tank is pretty full. I hooked up and fired the stovetop and all 3 burners had good flame.
     
  12. rabird

    rabird Howdy!

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    My furnace will run ya out if set high!

    The only reason I set my thermostat low is to conserve battery.
     
  13. kitphantom

    kitphantom Well-Known Member

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    Heat retention measures are a big help.

    Our furnace has worked very much better since we did the digital thermostat mod, as well as putting the new one on a long wire (with plug from Radio Shack), so it is on the counter instead of inches off the floor. We no longer have huge temperature swings, from freezing to roasting, even though we use the same settings we did with the original thermostat.
    I had to order a 'stat through Amazon, I could not find a non-programmable one that would operate in temps under 50 or so. While we keep it set (usually) in the mid-50s, it can be in the 20s or 30s when we start the furnace. I found reviews that indicated some just did not work a those temps. Ours is a LuxPro.
     
  14. timo4352

    timo4352 New Member

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    [SUN]
    My problem was a crappy thermostat. I replaced it with a known good one from my garage heater - that doesn't get used anyways. It works as it should now. My brother and I checked out the troublesome stat and it was 20 degrees out of calibration! Looks like someone messed with it before - probably ruined it - so in the trash it goes. I did have no problem warming up the camper to 70 degrees during my testing - it's about 55 outside today. I feel confident it will keep the inside 55 or 60 on a cool night now.
    Thanks for the replies.
     
  15. pej

    pej Member

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    I installed a Honeywell RTH221B1008 vertical model that was the same width as the old one.
    This one is similar:
    http://www.homedepot.com/p/Honeywell-1-Week-Programmable-Thermostat-RTH221B/203539508#.UmRsGflJOSo

    I wish I had purchased one with a backlight.

    http://www.homedepot.com/p/Honeywell-5-2-Day-Programmable-Thermostat-with-Backlight-RTH2300B/203539496#.UmRsw_lJOSo

    I really like kitphantom's idea of extending the thermostat to a counter top with a connector and wires. I could adjust it from bed!!
     
  16. tconroy

    tconroy Active Member

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    How many wires are on the thermostat anyway? I have a suburban but have never taken the thermostat off to look at it. [?:~{]
     
  17. tombiasi

    tombiasi Well-Known Member

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    Well, take it off and look at it.
     
  18. pej

    pej Member

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    Re: Atwood furnace cycles on & off

    Not sure about the Suburban as mine is an Atwood Hydroflame with a basic 2 wire setup.

    As for the connections, connect the +12v wire to Rh (heat) and the other to W. Basically the thermostat connects these two together when heat is required. Set the jumper on the thermostat to HG - heating with gas.


    Peter


    Sent from my ASUS Transformer Pad TF300T using Tapatalk 4
     
  19. tconroy

    tconroy Active Member

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    I will do that. I have to raise the roof up just to get the door open. Not much though just about 6 inches.
     
  20. tenttrailer

    tenttrailer Art & Joyce - Columbus, O

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    I have seen the same problem before. It was with the thermostat anticipator. Gently pull the cover off the stat. You will see a small slide or dial with numbers at the base of the lever that moved when you select the temp. Many time the factory does not set the antisitapor and it will be set to 0 or below. Move it to the highest number and you should be good.

    Now the question is what is the anticipator? It a small heater that is to anticipate the heat moving across the camper or a room that has not reached the stat and antispate the room temp before the heat reaches the stat. The correct way to set the anticipator is to disconnect the state and use a amp meter and measure the amps when the furnace is running and set the anticipator for that reading. Great to do this step for an insulated house, but an un-insulated trailer setting it to the highest setting works best.
     

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