Atwood 7920-II furnace failure

[breausaw]

My Atwood 7920-II furnace won't do anything, was working 100% perfect day before failure so something just broke.
No fan, no clicking, nothing.
Been reading tons of forum tech data relating to problem and watching YouTube.
What I've done or verified so far.

* 12v at controller, but no led light.
* fan motor works, jumped it.
* sail switch works, I've removed the furnace and checked continuity of the switch, replaced anyways.
* best I can tell the Thermostat works fine, has power and working contact switches.
* re-seated all connections.

At this point my guess is the controller is shot, ordered new on Amazon.

Just not sure what else I can try.

Thanks in advance for any Suggestions,

Jay

[dougrainer]

After 5 cycles what was the failure? Doug

[StirCrazy]

breausaw wrote:
Received new control board, installed and fixed problem; than quit working after about 5 cycles.
I bought the more expensive replacement on Amazon because it had better reviews but guess I got a bad one.
Amazon sending replacement.
At least I now the problem now.

Did you get a dinosaur board? They are about the best you can get. seams weird that it would run fine for 5 cycles though...

[breausaw]

Received new control board, installed and fixed problem; than quit working after about 5 cycles.
I bought the more expensive replacement on Amazon because it had better reviews but guess I got a bad one.
Amazon sending replacement.
At least I now the problem now.

[StirCrazy]

you can check for power and isolate all the main issues right off the bat. I had to do this in my 7016. check your thermostat to make sure it is letting power through, then with the wiring diagram you should be able to probe before and after the sail switch, then the same with the limit disk. Seeing as you're getting nothing, I am wondering if it is the thermostat. for me it turned out to be a intermittent issue with the board but it would still try to light..

[breausaw]

check for power coming into the circuit board at the blue wire of the connector.

This I understand, thanks!

Yes, power at blue wire thermostat on, no power off.
Feeling better about preliminary diagnosis. New controller board should be here Wednesday I'll post results.

Surprised to find out this circuit board has not been changed or updated since about the time RV electronic Ignition was invented, and it's has a long history of failures.

[trailrider]

If you have a 12 volt test light or a multimeter check for power coming into the circuit board at the blue wire of the connector. That will verify the thermostat is working and odds are the circuit board is bad. Not sending power to the fan motor.

[breausaw]

trailrider wrote:
If you have the newer version with the fan relay on the circuit board you need to check for power from the fan terminal to the fan motor when the thermostat is calling for heat. And make sure the thermostat is closing the circuit between the two white wires on this diagram.

http://techsupport.pdxrvwholesale.com/wp-content/uploads/2017/08/Atwood-7920-II-Installation-Manual....

Thanks for reply trailrider, this unit is about 20 years old so don't think it's a newer version. I'm not great at deciphering electrical diagrams, but can usually figure stuff out.
All roads seem to point to the control circuit board.

Unit is in a 06 Lance camper 855 we bought as old new stock 5 years ago. Was a trade in we bought from local dealer, the previous owner never used it, it was untouched like new throughout. Even through, all the appliances have had issues I've had to address except the stove which is analog, no electronics.

[trailrider]

If you have the newer version with the fan relay on the circuit board you need to check for power from the fan terminal to the fan motor when the thermostat is calling for heat. And make sure the thermostat is closing the circuit between the two white wires on this diagram.

http://techsupport.pdxrvwholesale.com/wp-content/uploads/2017/08/Atwood-7920-II-Installation-Manual....