If I switch the thermostat off the condensor doesn't stop and I can only make it stop by pulling the fuse block or switching the power switch off next to the air handler. I have removed the side of the condensor with all the power switched off and found no debret or webs and the contactor was open, when I switch all power on the contactor pulls in and the condensor starts but the tstat doesn't cut the low voltage to the contactor when it cycles?? If I remove one of the low voltage wires from the contactor, the contactor releases and the condensor shuts off. If I switch the tstat off the low voltage to the contactor is still on and the contactor stays pulled down? I have checked the 4 wires going to the tstat from the air handler and they are all hooked to the correct (Y G R W) without crossing, but someone has cut the lead outside the air handler and wire nutted the 4 wires together? When I remove the Y wire from the tstat the condensor doesn't stop but the air handle does stop. I'm thinking the problem is either my tstat or the wire leads have gone bad, but I don't have another tstat to try on it and need to ask if there is any way for me to test the thermostat to know if it is bad before buying one?