I have a Trane XE 80 gas furnace -it is blowing out cool air. I have it set on 72 it shows it is only 65 in the house. Is there a way to trouble shoot this before calling a repairman?

Air filter dirty?

Yes, look for a small viewing port in the lower section of the furnace. You will see a light blinking. Count the blinks and then remove the front panel. On the reverse side is a diagnostic chart that will tell you what the number of blinks represents. Let us know what you get.

It is blinking 4 times. thermal protection device open.

One of the sensors are getting hot and tripping. Look closely at the wiring diagram and follow the wires to all the safety sensors. I think this model has 3. One is found over the flame and has a rectangle mounting plate. Another one is is low in the burner box and I think there is one on the inducer blower. Test all of them using a multi-meter. Inspect them to see if any have a small reddish button to allow it to be reset.

Once you find out which one is bad, inspect why it went off and correct the issue. It could be a dirty air cleaner, slow room air blower or a venting issue.

I ended up getting an igniter. It's working great now.