I have a Trane XE80, it started to have a loud noisy sound and bad smell since about two weeks ago, then I found it was from the blower (didn't run when it has only cold air), and realize that the belt may need to be replaced, but the blower was working when heat air was push through.
Then I read the four flash lights, it indicated that the high limit switch was bad, it will stop the heat before it reach the set temporeture. And I ordered a new high limit switch, but this time, it get even worse, the call for heat didn't work, no clicking, first I think it may be the thermostat problem, but I jump between the R and W connect on control board, it still didn't start, should this mean a clean sign for bad control board, or it may be as simple as one of the switch was set to idle or turned off.
One hint, I did try to clean up the blower without unload it from track, could it touch certain switch, and force the whole system shutdown. Any idea, thanks.