I have a Carrier Weathermaker 8000 that is a furnace but also controls the AC from outside and the blower and everything int the house. I was told by last HVAC gentleman that the AC wouldn't turn off without turning the "Cut-off" switch off to the whole system, otherwise the AC continues to run without stopping. I actually rode it out like this for two years, testing out electric heat and yes my electric bills soared, but I finally bought the correct ICM replacement motherboard as he said I would need to correct the issue. I have put in the new motherboard, connected everything right as best I could and... its doing the same thing. I can actually get the heater to turn on (no gas hooked back up yet) but the AC is running too! I would appreciate any help! THanks! ZEE

Tell me about your THERMOSTAT.

https://www.thecoolingco.com/blog/st...-wont-turn-off

https://aristair.com/blog/ac-trouble...unning-system/

The thermostat is a "totaline" programmable thermostat that I can switch between cool, heat or off. The AC turns on and blows cold air even when the thermostat is turned off. I have to turn the kill switch next to themachine to stop the AC. I am glad I put in the next motherboard just as the old one was in, but disappointed that this didn't fix the issue. Bought a 200 board for nada lol. Oh well. Any help is appreciated.

The experts here can correct me if I'm wrong, but I would go to the furnace and where the thermostat wires go to the screw terminals there disconnect the RED wire.
If your unit still runs with this wire disconnected it would indicate a fault internal to the main board or furnace internal wiring, otherwise if it doesn't run it would point to the thermostat or thermostat wiring. ***updated***

Note: I'm a "handy guy"™ but not an expert.

Good luck,
WallyH