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ShotgunW 12-04-2010 11:09 AM

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.

yuri 12-04-2010 11:16 AM

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.

ShotgunW 12-04-2010 11:22 AM

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

hvactech126 12-04-2010 11:29 AM

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

ShotgunW 12-04-2010 11:36 AM

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

hvactech126 12-04-2010 11:43 AM

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....

ShotgunW 12-04-2010 11:47 AM

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?

hvactech126 12-04-2010 11:52 AM

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

ShotgunW 12-04-2010 12:00 PM

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

hvactech126 12-04-2010 12:04 PM

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

yuri 12-04-2010 12:14 PM

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

ShotgunW 12-04-2010 12:43 PM

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?

yuri 12-04-2010 12:46 PM

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

ShotgunW 12-04-2010 12:48 PM

No burn spots on back of board or anywhere.

hvactech126 12-04-2010 01:01 PM

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

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