On 4/9/2011 5:05 PM, Steve Turner wrote:
On 4/9/2011 4:52 PM, The Daring Dufas wrote:
On 4/9/2011 11:23 AM, Steve Turner wrote:
On 4/9/2011 10:59 AM, The Daring Dufas wrote:
On 4/9/2011 10:48 AM, Steve Turner wrote:
On 4/9/2011 9:12 AM, wrote:
On Apr 8, 10:05 pm, wrote:
On 4/8/2011 8:44 PM, Tony Hwang wrote:

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

...

... Buy one of hevier one(bigger size and really heavier in
weight than stock) If it blows again, something on the load side is
wrong.

I'd venture something is already wrong...

--

I'd agree. Responding to his first post and before he put this
latest transformer in I recommended measuring
how many amps are being drawn on the low voltage side.
This is electricity 101. So, he comes here asking for advice
and instead of listening, he justs puts another transformer in
and blows it too..... Go figure. Time to either get educated
or hire a pro.

In case you hadn't noticed, I've been getting LOTS of (much
appreciated)
advice from many people, but it's also been very contradictory with no
single suggested approach. It's been an interesting and informative
discussion, and I've been happy that nobody's been a jerk about it...
until *now*. And I DID listen; plenty of people suggested that the
original transformer was likely to be under-rated and to replace it
with
something more heavy-duty. Also, it seems to me that having a working
transformer is a pre-requisite to following your advice of
measuring the
amp draw on the low voltage side, no? Unfortunately, time constraints
prevented me from being there to perform those measurements when the
unit was running, and unfortunately again the transformer blew in my
absence. But of course, I'm repeating myself...


Steve I really hope you can figure out the problem with the furnace and
I can understand the bit about time constraints. Installing a fuse in
series
with with either side of the transformer is cheap insurance to
keep from losing another transformer. The fuse holders are inexpensive
and it's a lot less of a hassle to replace a blown fuse.

TDD

Yes, I would be more than willing to do that, but my electricity
training is not quite up to the 101 level that trader4 seems to think I
should have; can you suggest a specific fuse rating that I should use?
Thanks!


Most control boards have a place to plug in a low voltage blade fuse
just like
the ones introduced to automobiles by GM years ago. The value
will vary from 3 to 5 amps. A one amp fuse should be sufficient for the
primary/120volt side. The primary fuse should be installed in series
with the
black/hot wire of the transformer and the low voltage fuse should be
installed
in series with the red/R wire OOPS! I just noticed
something from the pictures of the burned transformer! The wire colors
in the control system of air handler/furnace wiring can vary a little
from manufacturer to manufacturer and I just saw something that may be
a problem causing confusion. The transformer in the picture has a YELLOW
wire in place of the RED low voltage output. The black/hot and
white/neutral
are for the 120vac connection and the yellow/R and blue/C
are on the other side of the transformer. The red and orange wires
should be
taped up because they are for 208-240 volt connections. If the
red wire on that transformer were hooked to the red wire connections
shown in
the wiring diagram, it will burn up. Yellow is usually the low
voltage wire color used for safety switches, pressure switches and
interlocks.
The blue wire is the common 24vac and is often grounded to
the metal cabinet of the furnace. A seasoned HVAC tech would have seen
the anomaly immediately and it wouldn't have posed a problem.

Not to worry; I read the directions. The red and orange wires were
indeed taped up and not used; only the white and black wires on the
input side were hooked up in the normal fashion. The blue and yellow
wires on the 24V output side of the transformer were hooked to the blue
and red wires (respectively) leading to the control board. I measured
input and output voltages after installing the transformer, and I
ensured that I was getting 24V on the output side before I hooked those
leads to the control board. The control board then came up with it the
flashing red LED to indicate normal ("no call for heat") operation.

Well, that blew that theory! ^_^

TDD