Trane XR90, LED flashes 2 times for error

theob

I checked and I don't have 24 volts across the gas valve. However, if that was caused by a trip from one of the switches, wouldn't that show up as three flashes of the led as opposed to the two flash, system lockout diagnositc?

theob

i took a quick picture of the upper portion of the furnace. i believe the switch at the bottom of the burner box is the high limit switch, and i checked that. the only think that i can think of that could possibly be the rollout switch would be the piece with two wires attached to it on the far wall below the burner box, but i don't see a reset button on it.

http://img543.imageshack.us/img543/1530/img4049j.jpg

beenthere

Pic is corrupted, and won't download.

theob

sorry. i'll post another version in a minute

theob

try this:

http://img18.imageshack.us/img18/2175/img4049q.jpg

theob

i uploaded a smaller version in case the link didn't come through.

Attached Images

 

beenthere

Should be a roll out on either the left or right side of the burner box.

That is the high limit directly below teh burner box.

theob

i checked and there is really absolutely nothing on either side, except for the pressure tube that comes off the bottom right (which you can see in the picture).

beenthere

Ok.

you said the red wire to ground had 24 volts. So trace the black wire to its source.

theob

the black wire is actually a blue wire and it junctions on a small-ish box to the left side of the circuit board that has 4 wires coming out of it. everything seemed to be connected/not corroded, etc.

beenthere

Trace those other wires.

theob

they all trace back to various places on the circuit board. i pulled each connection off the circuit board and checked for corrosion, etc, but i didn't find anything. i tried to fire up the furnace again to see if it was just a bad contact, but i got the same thing (nothing).

beenthere

I think your going to need someone on site for it then.

Just replacing parts until getting the right one can be expensive.

theob

i was afraid you were going to say that. do you think there's a decent possibility that it's the board itself? i found a place that i can get the oem replacement (a slight upgrade from the original) for a decent price (~$95) and i don't mind installing it myself. i certainly don't want to start replacing parts willy nilly, but i'm afraid that if someone comes by to fix it they're going to hand me a bill in the hundreds. maybe they wouldn't, but it certainly seems like a reasonable possibility.

i figured that at this point, it's not the ignitor, it's probably not the flame sensor (i cleaned it) or the pressure switch (i tested it), it's not the high limit switch (i tested that), i checked the pressure tubes, i vacuumed out the intake/exhaust outside the house.

is there anything i'm missing? i guess i don't know enough about what could go wrong here.

thanks again for the help. i really appreciate it, even if i don't solve the problem myself.

beenthere

Could be the board. But still sounds like something else.

Hate to see 85 bucks thrown away on a part that is not the problem. Then more money on another part. and then still have to call someone out.