On 4/8/2011 11:38 PM, David Nebenzahl wrote:
On 4/8/2011 8:22 PM Steve Turner spake thus:

On 4/8/2011 7:58 PM, David Nebenzahl wrote:

On 4/8/2011 5:52 PM Steve Turner spake thus:

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.

How 'bout installing an in-line fuse next time you replace the
xfmr? I'd put it on the secondary side. That way, if there is an
overload, the fuse will blow instead.

Thinking maybe I should spring for a transformer with a manual reset, like
this one:

http://www.pexsupply.com/White-Rodge...unt-14937000-p


Would that protect me from having to replace the damn transformer every time?
It looks like the circuit breaker is on the 24V output side; I'm a little
fuzzy on how that would protect the input side of the transformer...?

Why in the world would you think you need to protect the primary side?

Well I'm no electrician so I don't *know*. What I really mean is that I want
to protect *myself* from having to drop $20 or $30 a pop on a half-dozen
transformers while I'm trying to figure out what's wrong. So again, would the
transformer referenced above protect me from that? Many helpful things are
being suggested, but unfortunately they all seem to require testing the unit
while it's operational, and I can't do that unless I have a working transformer
installed.

Unless you've got a *really* weird problem--namely, severe overvoltage
spikes--there's no way the damage is coming from that side. It's got to be
because of overcurrent on the secondary side.

Ok, and how does that condition come into existence? Is there anything in the
wiring diagram that jumps out at you as a potential candidate? I have two
identical Trane AC/furnace units; one upstairs and one down. Should I swap
control boards between units to see if the problem follows the control board?

Unless there's something really messed up with your house's wiring ...

The house is only six years old. Nothing's changed in terms of wiring and
everything's been fine up until now.