What will make a transformer stop working on an air conditioner? Even if the transformer was brand new...?

Question

The transformer went out on my central air conditioner, so my brother-in-law replaced it yesterday. It worked like a charm until sometime today ( I was at work when it stopped working). What would make this happen? Thank you sooo much for any and all help!

Answer 1

Where are you getting these transformers? Are they real cheap? You can try checking the voltage supplying the transformer to see if your voltage is correct to the transformer. Just a shot in the dark I'm assuming your in the USA and your transformer is 60 hertz and not 50 hertz or vise verse. Is the transformer in the manufactured location and not moved to were hot air is blowing on it?

Answer 2

If in fact the transformer did go out and it is a correct replacement, some coil,contactor or relay is pulling too much current causing the transformer to burn out.

Answer 3

USA    First, make sure the correct transformer was installed.  If yes, check to make sure there is proper air flow around the transformer and the section of the unit it is in.  If a xformer gets hot, that will kill it.  Make sure the connections are made up tight.  Go back through the system, and check all neutral connections.  You might not have lost a xformer, you might have a loose or broken neutral or ground connection.

To verify, remove new xformer.  Hook it up temporarily to a temp power source, making sure the grounds are in place.  Test the secondary.  If you are getting voltage on the low voltage side, the xformer is ok and it is a connection inside the unit somewhere that is broken or loose.  You will have to back track through the system checking all the connections until you find the bad one.  Or, it might be a circuit board.  Try the xformer test.  If it turns out to be a good xformer, call a licensed HVAC tech.

Answer 4

You most likely have a short to ground someplace. All you can do is trace it down with a meter. If you checked the wall thermostat it could be there.

Relays can short but usually they don't work if they do, they don;t fix themselves.  A heat related short is rare.

Since it worked for a while it may be an intermittent short and those are tough. Places that happen is like where the 24v wiring goes through the cabinet. If not protected the vibrations of the blower will rub through the wiring and ground it. Same on the condenser end.  

Those shorts can be very intermittent.

The worst one to find for me was a case where the Tstat wiring accidentally had a loop of it in the vent through a small gap where the pipes connected and it was blowing around and rubbing. It would blow a fuse on the board about once a week. Checked good every time I put a meter on it.

Visually inspect all the visible low voltage wiring carefully. Particularly outside to the condenser. Weedeaters will strip insulation off those wires, it is not that strong.

And you can also wire in a fuse while testing. Boards use a 3 amp automotive type fuse. I have used higher ones, 5 and 7 amps and they protected my trans. enough while I was testing things.

Good Luck.