OK Guys, it was a very productive day, I think I may have finally solved my Atwood Furnace mystery.
This thing has just been bugging the heck out of me for 2 weeks now so I thought today, I go straight to the source.
This morning I called the Atwood Service Dept. I spoke with a Tech for almost 20 minutes. He told me one big thing that sort of answers a lot of questions. He said if the unit ever goes out on the high limit cut-out, it takes an hour before it will come on again. That is a full "Soft Lock" and the red light will flash at you. I have never had the flashing red light.
He thought on such a new unit, (remember, this furnace has less than 5 hours on it) doing all the things I described to him, it had to be a bad control board. He said the high temp switches "never go bad" He said go jump it and test the switch. He told me I had to go through a Factory Service Outlet to get the warranty on the control board. So I called my local RV dealership, one that I've bought parts from in the past. I spoke with the service manager, he really knew these furnaces, he said if the gas valve was only cycling off for 15-30 seconds it could not be the high temp limit, that would take much longer to re-set.
He said dealing with Manufactures on Factory warranties like this are tough, they never get paid back for all the labor it takes to diagnose and fix the problem. He asked where I bought the Atwood Furnace from and I told him E-Bay. He said if I bring the entire trailer in with my Visa card they would look at it. He said they need to run it inside the camper to get the whole picture, plus the Visa card was to put all the extra expenses that the warranty will not cover.
I told him I was going to double check a few things before I made a snap decision on this, I have a 2-year warranty on the furnace.
So I spent my entire lunch hour in the trailer.
Upon his recommendation I bumped the stat to about 70 degrees and sat down to wait it out. It was only 40 degrees when I entered the trailer. The unit ran and cycled the gas valve every 2-3 minutes off for only about 15-25 seconds and then back on. It did this at least 40 times. It took almost an hour to bring the trailer up from 40 to 70 degrees.
The supply air continued to rise as the camper warmed up and the return air was warmer going through the unit.
Finally the t-stat satisfied and everything shut down.
Then my next test was to jumper the high limit switch and see what happened. I unhooked the wires and jumped them together, the unit continued to cycle the gas valve exactly as before. After the furnace had gone through several gas valve on-off cycles again, I pulled the jumper wire off, the gas valve imediately shut down and the blower continued to run for a full minute or more. And now the red light was flashing a code at me. 1-flash with a 3 second pause = soft lock out. "Limit switch or air flow problems"
So Case-Closed on the high temp switch, that's not the problem.
I the decided that as long as I already had my face this far into the furnace that I would pull the ignitor and flame sensor out to inspect them.
To my surprise they were filthy, they were all sooty and black. I knew the flame sensor controls the gas valve as well, so I took some 220 grit sandpaper and cleaned them up.
I then replaced everything plus the wires on the high limit switch and started the unit.
It ran like a top and the gas valve did not cycle once, plus I noted that my discharge/supply air was the hottest it has ever been, about 122 degrees, granted, now the return air was at 68 degrees, so I figure the furnace has about a 55 degree temp rise. I can no longer hold my hand in front of the supply air for more than 5 seconds.
Could all these problems be from a sooted up or dirty flame sensor / ignitor?
I checked the troubleshooting guilde again and they mentioned that sooting could be a cause of low gas pressure. I had questioned my lp gas regulator so I replaced it last Saturday. But the old regulator could have caused the sooting and thus the faulty reading on my flame sensor and closing the gas valve prematurely.
Here are a couple shots of the ignitor and sensor, plus note how black the screw was that was holding the ingitor in place is?
As of now, I'm about 95% sure this the answer...I'm going to run it some more next weekend and check it out again.
Perhaps clean the sensor again just to be sure.
In a past life, I used to do HVAC service all over the Twin Cities area, and we would constantly clean or replace flame sensors on gas furnaces, I should have gone there right way, but with such a new unit I couldn't imagine that it would be this dirty already, so again, with the gas pressure not up to spec, that could have been the cause.
Gadget Man
