"dm440c" u44157@uwe wrote in message news:856ff33f86bde@uwe...
Hi, we have a 4 year old house and the upstairs AC thermostat suddenly
lost
it's display. I switched the thermostat with the downstairs one and the
problem stayed with the upstairs unit. I received a tip that the 240v to
24v
transformer might be the problem, so I went up to the attic where the air
handler is and tested the leads on the transformer... sure enough, 240v in
is
OK but nothing is coming out on the 24v side. So, I got a replacement
transformer and wired things back up. The display came back on, the unit
switched on and started blowing through the vents and I thought i had
fixed
it.

BUT about 5 minutes later i went up to check on it and the display had
gone
back out, so something is tearing up the transformers. I'm not an
electrical
engineer, but I can't figure out what would burn up a transformer without
tripping the main breaker. Any ideas?

Defective transformer, transformer voltage or current improperly rated for
the service, mis-connected, or overloaded. These transformers do not present
enough load, even when the secondary is shorted, to trip the main breaker.

Try another transformer, making sure it is for 240 volts and you have it so
connected. Some transformers have different leads for different voltages.
Also make sure the VA or current rating is at least what the original
transformer was. Monitor it carefully and if it seems to be overheating
check the secondary current to determine why it is overloaded.

Don Young