On 4/2/2011 9:49 PM, Steve Turner wrote:
On 4/2/2011 9:07 PM, Smitty Two wrote:
In articleTt6dnVBo95UBNwrQnZ2dnUVZ_qWdnZ2d@earthlink .com,
"Ralph wrote:

wrote in message
. ..

but it *could* mean that the transformer has a thermal fuse. If so,
it's
an easy and dirt cheap fix.

Smitty... All the transformers like that type that I have opened
have the
thermo fuse underneath the taping over the windings. I carefully get
to it
and add a 1 amp fuse in place of it. WW

Why a 1 amp fuse ? If on the 120 volt size, it would be over twice the
needed value and if on the secondary side, it would be too small.
Also it
would not be a thermal overload,but a current overload fuse.

Yeah, I'd say either bypass it or replace it with a new thermal fuse.
Putting a current fuse in there seems odd.

I just popped the covers on both transformers. There is no evidence of a
fuse in either one.

I made a mistake in my original description. I just metered the old
transformer and it's the input side that's bad, not the 24V output side
as I originally claimed. So the 115V input side is open on both the
original and replacement transformers, and the 24V sides are fine. I
think that rules out any load issues on the output side.

I must say, you guys have been very helpful! I've been a Usenet guy
since the mid nineties, but this is the first time I've had the occasion
to drop in on a.h.r and seek advice, and I'm glad I did. Thanks for all
the advice.

The fuses and/or breakers are always installed on the primaries of the
small transformers. The HVAC supply houses sell an external circuit
breaker used for testing systems so you don't have to keep replacing
transformers when servicing a system. :-)

TDD