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:

Simple. IF the motor is defective(IT IS in this case), the motor when it starts to draw too many amps will overheat and slow down. That causes 2 things. 1. The sail switch will probably open and shut the burner down. 2. The slower speed causes the burner case to also overheat and may cause the Limit switch to then trip. You can argue all you want about the parts replaced. In this case ALL the pertinent parts have been replaced and the only part left is the motor which is the ONLY part that will cause the CB to trip without a direct short. As with what Chris stated---Thermostats NEVER and rarely cause operational problems. ALL they do is open and close 2 wires to the furnace, nothing else. Doug