Hello all, this is my first post to the forums and I could really use some help. Last week my blower fan in the furnace/AC unit would not run. After some checking, I realized that the fan would run for approx 5 sec, then quit. No codes on the control board, solid red light. Then suddenly I had no lights on the board, totally dead.

Ok, I may have jumped the gun, I replaced the board without checking the voltage coming into the unit, same problem. I removed the cover from the door switch, and when I measure the AC voltage coming into the unit, I get 2.5v @ 60hz. WOW something is wrong!

Ok, so I checked the breaker, even swapped breakers, no change, so I have voltage into the house. Tracing the conduit back from the furnace I think I may have found the problem. the conduit runs from the breaker, into a box on my basement ceiling, like a switch box but with a small transformer on it, next to a switch in another box next to it. If it flip the switch, the voltage to the furnace goes to zero. Ok, so this mystery transformer is supplying voltage to what??? The thermostat maybe? There is a pair of brown small gauge wires coming off of it and running upstairs.

My guess is that the high voltage side of the transformer is shot, but what kind of transformer would this be and do I need it or can I bypass it and put the thermostat onto the 24v on the transformer inside of the furnace? Maybe this doesnt even go to the thermostat?

Any help would be appreciated as I need this fixed ASAP....93 degrees tomorrow and my wife isn't very happy!!!!!!!!!!!!

Thanks,

Brian