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kiakman's avatar
kiakman
Explorer
Nov 26, 2020

Atwood Furnace Issues

Hello all,

Have a perplexing Atwood furnace issue. This is an AC version. I have done a ton of research, troubleshooting and have the wiring diagrams and repair manuals. This is a new furnace and new installation. The furnace was working until I had to replace the squirrel cage (long story), in the process I think I caused a wiring problem, when one of the blue thermostat wires came out of the wire nut and shorted onto the metal frame of the furnace.

Now; I have 120v properly from the breaker, into the transformer, out of the transformer to the L1 terminal on the circuit board. That's where the power stops, no 12v on the blue thermostat wire on the circuit board TH terminal, no other power. The on/off switch does not change anything. Jumping the Thermostat wires doesn't do anything (both make sense because they have no power).

I have replaced the circuit board with a new Atwood unit. No change.

I'm stumped! Any ideas?
  • kiakman's avatar
    kiakman
    Explorer
    Dec 02, 2020
    Final Wrap up post,

    Thanks everyone for weighing in! Confirmed that this was the Transformer; if you are getting 120 to the transformer and no 12v or 24v out (depending on your furnace) than your transformer likely is fried and your circuit board may not have power as it is either 12v or 24v powered.
  • kiakman's avatar
    kiakman
    Explorer
    Nov 29, 2020
    Sorry for the delay. This is an Atwood/Dometic 38362 DFL35 120V.

    I had a senior moment and originally did not check for power coming out of the Yellow wire side of the transformer. I do have power on the black wire coming off of the transformer side, but not the yellow (24v) side.

    I would make sense that the board (and thermostat) is not powering up, if not receiving 24v from the transformer. So... I should have a new transformer to try early next week.

    Thanks for the other suggestions:
    - I did check the sail switch and it appears well.
    - To the one poster, there is not 'a fuse' on 120v units. So that others aren't looking for it, there is a breaker on source power and an On/Off switch only.

    Thanks everyone, all is pointing to me having blown the transformer. I'll report back.

    Since I have tried two circuit boards
  • dougrainer's avatar
    dougrainer
    Nomad
    Nov 27, 2020
    You replaced the impellor wheel. Now, on some model Atwoods IF the SAIL switch is non functioning, it will cause shut down of the Circuit board. Since the Sail switch is going to be disturbed when replacing the Impellor, make sure the Sail switch is connected and is not broken or "closed circuit" all the time. Doug
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Nov 27, 2020
    enblethen wrote:
    My old manual shows could be either 12 or 24 depending on model!
    Waiting for OP to post exact model number.


    AC Furnace...transformer can only change the voltage NOT convert it into DC
  • enblethen's avatar
    enblethen
    Nomad
    Nov 27, 2020
    My old manual shows could be either 12 or 24 depending on model!
    Waiting for OP to post exact model number.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Nov 27, 2020
    AC Model.....should be 24VAC to/from thermostat
    Transformer drops the 120VAC down to 24VAC ----no 12VDC

    What is the MODEL number of this NEW Furnace??
  • BFL13's avatar
    BFL13
    Explorer II
    Nov 26, 2020
    Should be easy. Blue wire is 12v and was shorted to frame, so find the fuse and replace.
  • enblethen's avatar
    enblethen
    Nomad
    Nov 26, 2020
    Model number of furnace?
    I hope you do not have 120 volts on the circuit board! It should be 12 volts coming out of transformer between the yellows.
    I am looking at diagram for 8900-III

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