Heater wonít light up indicating Air Flow / Limit Fault - How to fix?
My Atwood heater for my 2018 Thor Freedom Elite 24FE Sprinter is not igniting consistently so often I must use an electric heater as my main backup option, but not so well when itís 39 degrees outside in the middle of the night. I have checked all the main fuses in the cab and the panel under the bed and all were fine. I have opened the outside compartments and hit the reset button and occasionally the propane will fire up and thus temporally work but the next day or two it wonít. The fan will generally always go on for 20 seconds when testing but then usually shuts off before the propane flows and fires up. The light indicator on the circuit board is lighting up 1 time every 3 seconds which on the fan motor they have provided a summary chart indicating ďAir Flow / Limit FaultĒ but I can find no limitations to the air flow, it appears to fully flow and does occasionally work. Below are a few pictures I just took but Iím not sure what else to look for or do. I can see no water or moisture anywhere in the fan or heater compartments nor any on the circuit board or electronics. The batteries are fully charged and donít appear to be the issue. Itís getting power, there is a full tank of propane and it occasionally works, just not consistently. I am now suspecting the sail switch is not functioning correctly as Iíve read the fan goes on for 20 seconds so the air flow will trigger or move the switch so the propane can then flow and fire up but I donít know where the sail switch is to observe if it is sticking or not. Iíve read many point out basic items like fuses, power, circuit board wet or defective but then why is it on occasions working properly, which leads me to the sail switch but what do I know . Can anyone help, canít get it in for servicing until 3/19 and itís been very cold here lately.
Just a quick guess here, but from your description it sounds like the sail switch is not proving air flow is good (even though you feel air blowing for that first 20 seconds) to the control electronics. If the electronics does not receive the air flow confirmation it will not open the gas valve and continue with the flame start process. If the sail switch is bad or not free to move when the blower first starts blowing (after thermostat calls for heat) then you need to check that first I suspect.
Is the sail switch observable? Iím not sure where it is although I saw schematics for older Atwoodís that shows it but if itís observable I may need someone to guide me to it or circle it on my photo. Iíve used an air blower to try and clear dust etc. but still not generally working. If the sail switch is observable and easy to reach I could try and make sure nothing is clogging it or impeding it but Iíve never heard of a sail switch before so Iím not exactly sure what to look at.
I think on some furnaces the sail switch is easily removed, but of course not on all. I am not familiar with your coach specifically but I am attaching a YouTube video on one that is easily inspected for function/operation....probably many of them are in a similar physical position on the blower unit. One thing you could try is banging the side of the fan housing when the thermostat calls for heat and motor is running in those first 30 seconds to see if the banging frees up the sail switch enough for the full gas start sequence to complete. The other is bypassing the sail switch electrically at the correct time in the start sequence, but I won't suggest doing that unless you are electrically knowledgeable. (could cause you more trouble otherwise).
That was it! Thank you very very much! I did exactly as shown in the video you provided which showed opening the sail switch and cleaning out strands of dust preventing the switch from operating properly. Mine was only about half as dirty but one strand was in a position to block the switch which I easily removed and then I cleaned out a second strand just inside the opening and Iíve tried it several times and it now appears to reliably light up and ignite. Awesome, my chilled body thanks you again!
Yes, the hardest part of doing the inspection and then cleaning any dust or debris that has built up and blocking proper function of the switch is removing the 10 screws on the cover to the compartment and then removing the 2 screws to the sail switch which is right in the middle of the fan with two blue wires connected and then screwing them back in. It takes less than 5 mins to fix, once you know what to look for and easily do. I feel more confident every time we learn how to do these fairly simple but often important fixes.
glad you got itworking.
i have a 2017 fe29 with the exact same furnace.
if you look on the blower housing, there is a chart that tells you how to read the control
1 blink every 3 secs is no air flow.
i am currently waiting for a replacement airflow "sail" switch.