Thursday, September 15, 2011

Changed Thermostat / AC Compressor wont shut off...?

Helping a friend with a central AC. He has already swapped the thermostat, switch and transformer. The fan in the AC unit in the attic turns on when the thermostat is set to cool. Unfortunately, the compressor outside runs non-stop. I flipped the circuit breaker to stop the compressor. In the attic I noticed a white and red wire coming from the compressor to a panel. At this panel the white wire (from the compressor) is connected to the 24v lead from the transformer and one leg of the switch. The red lead is spliced to the %26quot;Y%26quot; wire coming from the thermostat. The thermostat was a newer Honeywell electronic model, it has been replaced by a much cheaper Honeywell version. The only other info I have is, there was a jumper wire on the original thermostat. The currently installed model doesn't have a jumper wire.

Any suggestions on why the compressor wont shut off? The line going outside also freezes over after 3-4 hours of running. Airflow is good, compressor was charged last year.
Changed Thermostat / AC Compressor wont shut off...?
only three possible reasons for this to happen....1 yellow wire that hooks to red wire going to condensing unit is not on the y terminal on the thermostat...2 bad thermostat..3 contactor is burnt shut especially if this is the problem he had when he started doing all the parts replacement..
Changed Thermostat / AC Compressor wont shut off...?
Since you have checked all the low voltage wiring, it seems that the problem is in the outdoor unit. It is rare but the contactor in the outside unit could be stuck shut. It is easy to check and you should be able to tell by looking at it.
sThe red and white wire were just used as a leg to the contactor of the condensing unit. White would go to common and red to yellow( cool) from the thermostat. You may not need any jumper as the two stats are configured differently. If the condensing unit stays on , first disconnect 1 wire at the condensing unit ( low voltage) if unit goes off you have a incorrect placement of low voltage wiring into thermostat. recheck using wiring diagram. good luck