I've been servicing heating and cooling equipment on and off for quite some time now (I run a boiler operations company and I work on smaller ones if it looks like someone is really freezing), but I can't seem to figure out my current problem. A couple of years ago I had a contractor install the following Furnace in my house:
The furnace is currently short cycling due to overheating. The furnace runs fine if I remove the lower access cover (where the circuit board is). It takes this much air flow to prevent overheating. It doesn't even run if I leave the filter access open. It needs the full access cover for the circuit board. Could the high limit switch fail in such a way as to cause the furnace to trip out at a lower than desired temperature? Is there any way this could be a thermocouple?
I'm thinking about just replacing both the thermocouple and the high limit. Any opinions would be welcome, especially by email.