Atwood 8500-IV furnace problem

DFord wrote:
So far, I've seen no indication that anyone has any idea of why the furnace is short cycling when it should be off. I've given a suggested procedure to begin troubleshooting but everyone just wants to swap parts. All the parts changed out so far has just been a waste of money and nothing has been accomplished.

I've studied the wiring diagram and see the thermostat only has two wires going to it. When the thermostat calls for heat, those two wires are connected. When it's not, those wire are disconnected. Until you know why the furnace is short cycling, the reason for the breaker tripping is a secondary symptom of the actual problem. A bad blower motor could not possibly cause the furnace to short cycle.

I would disconnect the thermostat and use a jumper to run the furnace for a couple of minutes. Then remove the jumper and see what happens. The furnace should not reignite again. What we need to know is if the thermostat is causing the furnace to short cycle. The OP stated the furnace reignited when it was short cycling. If that's the case, the thermostat is the cause of the problem. If only the blower is short cycling, the problem is probably the "relay."

"RELAY" description from the furnace manual wrote:

Don. I have been pondering the same thing. I can understand that excessive current draw of blower motor would trip the circuit breaker. But I don't understand why that would cause the furnace to cycle on and off like it does before the breaker is tripped.
I like your suggestion of trying to by-pass the thermostat and see if the problem continues.
Thanks for the insight.
Carl