My transformer blew on my furnace, I replaced it with a tranformer with inline fuse. The furnace worked, but when I tested A/C the fuse blew. I replaced fuse and furnace still works, but I haven't tried A/C again. What are the probable causes for the A/C to blow the transformer?

I recently encountered a situation were I was blowing my accesory transformer on my furnace whenever I would turn my thermostat to the A/C position. It turned out that the transformer was wired up incorrectly and it was getting an induced voltage (220 volts) from the (unsused) blower motor winding which was blowing it up. Does the transformer blow with no load on the secondary ? Do you have a voltmeter that you could use to monitor primary voltage ? What is the transformer used for on your system ?


Morrowrj

You probably have a bad 24 volt coil in your condensing unit. Your transformer usually supplies all of the control voltage to your outside unit. It's not uncommon to have a bad coil in your contactor. If you don't have a volt meter you can go outside and turn off the power to the condensing unit, unhook the two small wires that go to the contactor, be careful they don't touch anything or each other. Go back inside and try to run the AC, if the fuse doesn't blow you have a bad contactor coil.

Besides the coil, the wires themselves could be shorted. I have had different problems with mine being chewed. I armored them.

http://www.photolocker.net/images/Labman/KatetheAC.jpg

Thank you all for the help! The problem was the wires from the A-C to the transformer shorted outside. I don't know how it happened since I don't have pets, but I replaced it and now my A-C and furnace works great. Thank you again