I have a carrier central air conditioning unit in a house that I just purchased. I was working on the house recently, and since it was a nice day decided to turn off the furnace and A/C. A few moments later the A/C kicked on. (system switch is on off). After futzing with the thremastat for a while I determiend that the heat/of/cool switch might be a bit warn and not sticking in the off position properly. I decided to replace the thermostat with a brand new hunter model (assumed it would do the trick). To my amazement - (with the system on off) the air conditioning unit kicked on again (condenser and all). I know that the system is wired correctly. And the Heat and Cool function properly when in their respective settings. Any suggestions??

Where is the "System Switch" you are operating? The furnace may have it's own separate control circuit from the AC unit, and you are only shutting off the heat.

Where is the "System Switch" you are operating? The furnace may have it's own separate control circuit from the AC unit, and you are only shutting off the heat.

The system switch I was speaking off is the one located on the thremostat. I would assume when I switch the thermostat to off, that neither the furnace nor the AC should opperate. Is that not the case? Right now I have the AC shut off at the breaker (only way I could stop it from running with the thermostat in the "off" position). Thanks for your help!!

You are correct to assume that the entire system should shut down by shutting off the system switch. Perhaps the stat is defective, or miswired. If all works well, and you know to shut off the breaker, which I am sure is a nunsance at times, I see no problem leaving it that way.