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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

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The outdoor unit's contactor is welded shut, most likely

My first port of call at this point would be to check the contactor in the outdoor unit that turns power to the compressor on and off based on the Y signal from the thermostat -- if the contacts on that are welded shut, then the air conditioner will run constantly no matter what the thermostat and control board have to say on the matter.

  • YouTube has plenty of test ac contactor videos, might even be able to see & hear the switch clicking shut & open, or manually move it (carefully, with something insulated) – Xen2050 Oct 6 '18 at 0:15

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