"Steve Turner" wrote in message ...

A continuation of the "Why does the 115V-24V transformer keep
blowing on my Trane XB80?" discussion I started on 04/02/2011.

Yep, My A/C unit blew another transformer. Pictures (and wiring
diagram) he

http://www.flickr.com/photos/bbqboye...7626457562742/

Trane's manual for the unit is here (for perhaps better viewing of
the wiring diagrams that I also copied to my above flickr site as
jpg images):


http://www.trane.com/webcache/un/fur...7_04012009.pdf

As you can probably see in the pictures, there is visible charring
of the 115V leads going into the transformer, and of course the 115V
circuit is open (again). If you didn't see my first thread, this is
the third transformer the unit has blown. In the previous
discussion, it was discussed that perhaps the first one just blew
because of old age (6 years), and the second blew because it wasn't
a proper replacement (poor quality, made in China, etc.). This
third unit is most certainly a proper replacement, and it's most
certainly indicative of a real problem I have somewhere else in the
unit. I didn't see any such charring on the previous two units, at
least not like this.

I never got a real chance to test out the system after installing
this third transformer. We had cool weather for several days, and I
never tried to force the system to come on so I could monitor it;
that was probably a mistake. Unfortunately, I was also absent from
the premises during the extended times when the unit was most likely
operational, so that didn't help either. However, my family tells me
that it WAS working and cooling the house rather nicely, for at
least a day, perhaps two. I'm getting 115V in all the right places,
so it doesn't look like an over-voltage condition to me. Perhaps
it's an overheating condition? It looks to me like the only real
load on this circuit is the blower motor; could the motor be causing
this? The blower spins freely when I turn it by hand. Start
capacitor on the motor maybe? Relay on the control board perhaps?


Just a thought,

When you put the new transformer in does the "Diagnostic Light" LED
turn on ?
Does the LED blink or flash in one of the patterns indicated in the
"diagnostic codes" section that you posted a link to ?

The "diagnostic codes" imply that the control board can detect
several of the problems mentioned by others.
Maybe a good starting point as there is not enough time to test with
test equipment.

robb