I have a Trane XR80 gas furnace. While the blower and the vent fan are running, only cold air is coming out. After some study over internet, I found that the temperature in the furnace went up too high for various reasons (clogged air filter.. etc.) and the circuit is open, not closed. To make it reset, all you have to do is tapping the "Limit Switch (bimetal device)" with a screwdriver to have the bimetal go to its original position. It would be too expensive to pay $80 minimum trip charge to a pro for this. Please share your knowledge with me if you have any idea.

My Question : Where is the "Temperature Limit Circuit"? In Trane XR80?

Actually the device you are talking about is a SAFETY device. Now it may be to expensive for a service call but is it to expensive to replace the part to continue the safety of your family? Tapping or banging on a safety device to get it to operate is not my idea of a repair. Replace the switch before bigger problems happen.

Where is the "Temperature Limit Circuit"? In Trane XR80?