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Bulletboy's avatar
Bulletboy
Explorer
Jun 13, 2020

FURNACE PROBLEM

Hi, I have a 2015 Keystone Bullet with an Atwood (AFMD30121) furnace.
It worked fine, then through the night stopped working...the blower kicks on for 30sec then shuts off with no ignition.
The circuit board blinks with a code stating it’s an Air flow/Limit Fault problem.

I’ve taken the sail switch out and everything is clean. I put an Ohm meter on it and when I manually close the switch it reads 3 Ohm...then drops to 0 within a second.
When I check the Ohms with it in place...just reads open line the whole time (With fan on)

I’ve then checked the Voltage going to the Sail Switch and 1st time read 12V at the wire...but 0 when it’s plugged into sail switch. I then tried again to measure voltage (with fan on) and can’t get any reading at all?!?

At first I thought my sail switch is faulty...but now I’m wondering if it’s the circuit board. I find it strange that I can’t get a voltage reading now, especially when I was getting one...even when the furnace wouldn’t ignite.

I have the furnace pulled out and there is no sign of dust/debris anywhere

Your response & thoughts are all greatly appreciated! Thanks
  • Huntindog's avatar
    Huntindog
    Explorer
    Jun 14, 2020
    Bulletboy wrote:
    Hi, I have a 2015 Keystone Bullet with an Atwood (AFMD30121) furnace.
    It worked fine, then through the night stopped working...the blower kicks on for 30sec then shuts off with no ignition.
    The circuit board blinks with a code stating it’s an Air flow/Limit Fault problem.

    I’ve taken the sail switch out and everything is clean. I put an Ohm meter on it and when I manually close the switch it reads 3 Ohm...then drops to 0 within a second.
    When I check the Ohms with it in place...just reads open line the whole time (With fan on)

    I’ve then checked the Voltage going to the Sail Switch and 1st time read 12V at the wire...but 0 when it’s plugged into sail switch. I then tried again to measure voltage (with fan on) and can’t get any reading at all?!?

    At first I thought my sail switch is faulty...but now I’m wondering if it’s the circuit board. I find it strange that I can’t get a voltage reading now, especially when I was getting one...even when the furnace wouldn’t ignite.

    I have the furnace pulled out and there is no sign of dust/debris anywhere

    Your response & thoughts are all greatly appreciated! Thanks
    The sail switch is the most common thing to fail. So much so, that I carry a spare.
    They cost under 10.00.
    The next most common thing is the factory circuit board. The dinosuar board is a big step up in quality... But costs over 100.00.

    So I would replace the sail switch first, and if that doesn't fix it, then replace the circuit board. Worst case is you end up with a spare sail switch. Not a bad item to have around.
  • Thermoguy's avatar
    Thermoguy
    Explorer II
    Jun 14, 2020
    I had the same problem you are experiencing and it was my igniter. I didn't troubleshoot it, I took it to a RV repair and they replaced it. I'm not sure if the "sail switch" is the igniter, so I apologize for my ignorance. But, that was the fix for mine.
  • Huntindog's avatar
    Huntindog
    Explorer
    Jun 14, 2020
    Thermoguy wrote:
    I had the same problem you are experiencing and it was my igniter. I didn't troubleshoot it, I took it to a RV repair and they replaced it. I'm not sure if the "sail switch" is the igniter, so I apologize for my ignorance. But, that was the fix for mine.
    The igniter is different.
    They hardly ever fail.(not saying it is not the case here, just that it's not where I would look first)
    The sail switch is triggered by the fan blowing air thru the unit (hence it's name) When it fails, the gas will not flow, and the igniter will not spark. This is to prevent a bad meltdown if the fan motor should fail. You simply cannot have the furnace burning without air flowing thru it to carry away some heat.

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