Trane XE 80 Control board fuse blows
 

Hello, I have a Trane XE80 approx 16yrs old. When heat is turned on, fuse on control board blows on call to heat. Unhooked W at control board and jumped R and W at stat no blown fuse. Hooked w up at board jumped at board blown fuse. Checked high limit switch it checked okay. What is the next logical step to diagnos this problem? Have ohm meters etc.

Start over. Remove w at the board and then jumper r to w on the board. Sounds like you have a shorting w wire from the tstat. If you leave it on and jumper r to w it is still in the circuit.

Will do this in a moment. Thanks i will post what happens.

it sounds like bad stat or in stat wiring, short to ground on w

Removed W at board, Jumped r to w, as soon as it touched blew fuse, what next?

just to verify, you removed the white wire and then jumpered r to w and it still blew the fuse, if you have access to one, a 3 amp breaker will save you money on fuses. there is a control or safety circuit wire that is shorted to ground, this would be inside the furnace....

Don't have breaker so a short to ground inside furnace. Is this a visual find or what would be the steps to locating it?

pretty much gonna be a visual find.. when you checked the high limit, you did put it all the way back in the furnace with the screw, right? IF NOT THAT COULD BE CAUSE OF SHORT. Check for pinched wiring where doors hook on

Yes, high limit is mounted and screwed in. Could this still be a stat problem or did previous test eliminate that possibility?

yes last test proved stat not problem, but to make sure you can remove all the wires at the control board from the stat and jumper w to r and if it blow the fuse you know for sure with out a doubt its in the furnace

Visually carefully look for any wires which could be touching the exhaust fan. If they did and melted that is a common short spot.

Unhooked all stat wires at control board, jumped R to W, blew fuse. Checked all wiring could not find any melted or other wise shorted wires. Any suggestions?

Take the board off and look for burnt spot underneath it and on it.

No burn spots on back of board or anywhere.

from this point, call a pro, hard to suggest anything else without sitting in front of it, definitely a short though