Greetings, and thanks for your help/advice ahead of time.
I came home fromthe weekend to find a hot house, and a frozen coil. Funny part is , it isn't the usual suspect.
For some reason, the compressor and fan outside the house will not shut off. I have a digital programmable tstat. I tried turning the A/C off, fan off etc. The air handler turns on and off when appropriate by temp, but the compressor doesn't. Subsequently, the coils freeze up. So far the only way i can get the compressor to turn off is by switching the breaker on the outside of the house.
so, is this most likely a faulty tstat? is there a relay of some sort, like the one that turns on the fan in the air handler? (replaced that 3 months ago.)
What is a good troubleshooting technique?
I know I can replace the tstat, but would like to troubele shoot it first.
thank you
john

 

Could be tstat or tstat wires to the unit.First turn power off, to outdoor only.look and see if the "relay or contactor"same in outdoor unit is stuck on ,could be this. With power off ,tstat calling for cool. pull a low volt tstat wire off the relay, it should open. If not get a new one just like it. ED

 

contactor probably stuck. it is located in the outdoor unit, it is the part the power wires terminate into. it has an electromagnet that pulls a set of points together, and many times these points weld together causing the outdoor units to stay on