Bench Testing Atwood AFSAD12121 Furnace

[Traildad]

As I mentioned in another thread I am having problems with the furnace in my 2015 Escape 19. I had to pull it into the interior of the trailer to work on it. I got a universal barbecue propane hose and a Stansport double cylinder fuel post so I can supply propane to the furnace while it is sitting on a TV tray in the trailer. I have done some testing and I am thinking it is the overheat switch or possibly the fan is weak.

When I turn it on after about 15 seconds the igniter fires and the propane comes on and it lights and gets hot. Then it runs for about 3 minutes and the propane turns off and the error light gives me a one flash error code which is Air Flow/Limit Fault. There is a white plug on the circuit board with two blue, one red and one black wires. While it’s working the two blue and one red wires show 11 volts. When the gas shuts off the red wire and the blue wire closest to the edge of the white plug lose power. When the fan starts running there is 11 volts present on both terminals of the sail switch. When the propane shuts off there is still 11 volts on both terminals of the sail switch.

This suggests to me that the sail switch is working and has not cut power to the system so the problem must be elsewhere. I’m trying to test the overheat switch but it is deep in the furnace and next to the hot exhaust so it is difficult to test. I guess I should replace it and hope since it is cheaper than replacing the fan.

Anyone have any ideas or suggestions?

[Traildad]

I think I might have found the problem. It’s hard to see and I don’t know what it’s supposed to look like. I took the panel off where the hot air blows out to heat the trailer. You can see the tubes that get heated by the gas which transfer heat to the air coming from the blower. I took some photos but they aren’t great in the difficult to see area.

[Traildad]

I can’t see very well but it looks like there is a piece of sheet metal blocking the air flow. That makes sense. Insufficient air flow would cause it to overheat. Late at night when it gets colder it might be harder to make it overheat so it keeps running.

[Traildad]

I opened up the case some more and it seems like there is one screw holding it in. Is that piece supposed to be in there like that?

[Eggscape]

That metal does not look right at all.
However I would be concerned that when the fan runs it drags the voltage down below the 11 you are seeing.
When plugged in our trailer shows 13.3 volts and I would think that yours should show similar.

[Traildad]

Ok I guess this just doesn’t want to be easy. One of the screws holding in the High Limit Switch would just spin around when I tried to remove it. Even pressing on the pointy end while trying to remove it didn’t help. I had to take the furnace out of the case to get enough access to remove the screw. While I had it apart I also got better access to the piece of metal that was hanging in front of the fan blocking air flow to the heat exchanger side. The first photo shows how it was positioned and the second photo shows how I think it is supposed to be. As you can see the two holes line up with the holes in the case. Before they were just pointing to nothing. With that perfect alignment for the holes I decided that is how it is supposed to be rather than blocking the fan and flopping around inside the furnace. I hope I’m right. Since I’ve replaced the high limit switch at the same time I won’t know for sure.

[Traildad]

I think I fixed it. It’s still in the bench testing phase but I put it back together and it ran for 10 minutes without stopping or flashing any error codes. The longest it ran on the bench in the beginning was 4 minutes. I think even less if was already warm.

[Traildad]

I reinstalled it in the trailer and it looks to be working correctly. Keeping my fingers crossed.

[iamunique127]

That is a tricky bit of trouble shooting. Great work.

[Ryanb-72]

Well I would like to offer my thanks in advance for your posts with updates!
We just got back from a several thousand mile trip and of course the heater did not work when needed....
Not sure what exactly is wrong but your posts gives me an idea of where to start looking.
Thanks