atwood furnace not coming on

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rbTN

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In my (new to me only had it 4 days now) 2007 Denahli 26RL I have an atwood 8531-IV DCLP furnace. Last night I was working in the trailer for a while so turned on the heat. It came on fine, warmed up the place and kicked off. I noticed later it seemed cool and sure enough the furnace should have come back on. I checked fuses, the tstat powered the fan, had gas at the range, so I opened the furnace cover. The light was flashing once, then off for a few seconds, then a single flash, repeat. This I think indicates an air flow issue. I'm guessing it is because the fan is not coming back on. I was putting the cover back on and almost dropped it, bumping the furnace and the fan came on! Burner lit, warm air blowing, stayed on till it was about the set temp and went off. When the temp got low enough for it to come back on it did the same thing, never came back on. Checked again and same flashing light. So i tried it again, a slight bump to the furnace and the fan came on and worked like it should.

So I'm trying to determine what the real problem is. At first I though some loose wire but I can move all the wires without it coming on but as soon as I give it a bump, it  starts.

Would a sail switch staying stuck on (in the position it would be if the fan was working) cause this? Any suggestions on what to test for or look into would be great.
 
I would think that it would....Can you see where the sail switch is located??
 
from what I can tell, it is on the back side of the blower housing, at least thats where the wires go.

I should have added, i did not have time today with it raining to actually do anymore troubleshooting. I need to get a meter on it and see if I can tell what switch is sticking, if one is. I don't think its the motor, it runs fine when it comes on, no noise or vibration.
 
First thing I would do before replacing anything is to go through every blade connector in the furnace and take them apart and reconnect them a couple of times.  It doesn't take a lot of corrosion to cause a bad connection.  Also disconnect and reconnect the edge connector on the control board a couple of times.
 
I think we're overlooking one key point here... The fan motor is NOT coming on, and the sail switch does NOT control the fan motor. The sail switch controls the gas valve and ignition sequence AFTER the fan is up to speed and the air flow closes the sail switch. Wally's advice is exactly where I would start.

http://direct.bryantrv.com/docs2/docs/hflameservice.pdf
 
For some reason I believe Atwood used 2nd's and the blower motor may have a dead spot.. Same with the electric steps. the Temp cure you discovered (A bump) THe long term is a new blower motor. the replacement motors are 1sts (no dead spots).
 
If cleaning the connections doesn't help, then next, I'd take a meter to the delay relay. I recently had the same malfunction as the OP, and that was the part I found bad.
Same symptom.  Turn the furnace on, and raise the temp.  I could hear the relay in the power management clicking, but the furnace wouldn't run.  Had power at the 2 input legs of the delay relay, and ground at the 3rd as should be, but no power to the 4th wire going to the fan.  Jumped the relay and the blower spun and the furnace fired up. I changed the one on my 8535-IV with one from Dinosaur.
 
It's not the sail switch, for the reason NY_Dutch stated.   


The single flash code means the High Limit Switch has opened (furnace burner chamber overheated).  That can indeed be caused by a lack of circulation air flow (the air that flows through the furnace and out the interior ducts), but the fan should continue to run after the Hi Limit trips. Hi Limit shuts off the gas supply but leaves the fan running to cool it down. If your fan was off, you have either a bad wire connection or a bad fan.  The fact that a simple bump got the fan turned on again says much the same thing.
 
I hate to say something is fixed, when I didn't "fix" anything, but I started by taking the blower connector off the board and applying 12 v to the motor and it spun up without hesitation. Then I pulled the board out, took off all connections replacing them all a couple times, checking the terminal ends in the process. Pulled the connectors off the power switch multiple times. Put it all back together.

It has been running fine for over 4.5 hrs so far tonight. I don't know if I found a loose connection or a bad connection but it seems to be working so far. I'm going to let it run tonight and see how it does.

thanks for all the info - I'll let you know how it goes
 
Most likely you effectively cleaned some corrosion off the contacts, correcting the problem. I'm glad it's working for you, and hopefully it'll hang in there now...
 
NY_Dutch said:
Most likely you effectively cleaned some corrosion off the contacts, correcting the problem. I'm glad it's working for you, and hopefully it'll hang in there now...
Click to expand...

YEAH What he said.
 
I left it on overnight and put a thermometer in there that stores the high and low temps. It kept it within 7 degrees of the set temp all night. So I guess I'll consider it fixed. I may go through it all again and re-crimp terminal ends etc this weekend just to be sure.

thanks again.
 
It is possible it was a bad connection Also possible there is a short (I seem to have one in mine from time to time.. Long story as to how I know that) but if bumping fixed it. I'm going with a blower motor issue.  Seems to be my problem too but since I know how to make it happy.. And I mostly use electric heat.. I'm not yet into fixing it.
 
follow up to this problem, and hopefully a resolution...

The furnace continued to act up, some times it would cycle fine for hours then just stop working. A good bump to the black frame of the furnace (outside cover off) would get it working again. So I took it apart and started checking things. I could not get an indication of either the sail switch or the high limit being a problem and all connections seem clean and solid. So I just ordered a replacement sail switch and high limit. Put them in and it cycles fine so far.

I'll post another follow up later to confirm it is corrected.
 
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