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czars 04-16-2013 07:14 PM

Step Down Transformer
What kinds of things can cause the 240V/24V, 40VA transformer to burn up? My A/C service guy has no clue.

ddawg16 04-16-2013 07:29 PM

A short.

Use an ohm meter and measure the load.

52Caddy 04-16-2013 07:46 PM

Short would be my guess too. Overloaded too, might have caused a breakdown inside causing the short.
I've seen them go bad in our commercial installs, but not very frequently.

beenthere 04-16-2013 07:46 PM

There is a short in the low voltage somewhere.

ben's plumbing 04-16-2013 09:24 PM

1 st get a new a/c service guy....then look for short..ben sr

hvac instructor 04-16-2013 10:11 PM

which side burned up, primary or secondary

old_squid 04-17-2013 11:29 AM

The reason for a transformer failure are most times the hardest to find. They usually fail due to a short in the low voltage wiring somewhere. Because of the low voltage and low amperage the short doesn't jump out and say "HERE I AM!" like high voltage shorts do. No burns or arc marks to help you find the cause leaves you usually tracing every inch of wiring especially wherever it gets close or touches metal.

Then of course there is always the inquisitive teeth of rodents and dogs that sometimes will kill a transformer.

If your service person did a good inspection of every bit of wiring that the transformer supplies and still shrugs saying he has no idea, then he just did what every service tech has or will do in his entire career. What he does next though is what will identify him as either a parts changer or not.

A short that can't be found should be followed up with the installation of a fuse for starters that protects the transformer from future failure due to shorts. That's if there isn't already one installed. The next thing that should be installed are what is called Tattle Tales. These are electrical devices installed in certain areas of the wiring that if the short happens again will at a minimum tell the service tech exactly what section of wiring the problem is in.

Is the fuse and Tattle Tales going to cost you? Yes. But you already paid to have one transformer replaced without a clear answer as to why it failed.

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