2000 Durango SUV AC "always on"

Our SUV has a slight air conditioning problem. The compressor is always on, regardless of switch position. Only way to turn it off is to unplug at the
harness near the unit. It blows really cold air. Having the unit on all the time causes the hot air to be just warm, so it was disconnected all winter, with summer starting here in Seattle we would like to get it fixed. One of the odd symptoms of the unit running all the time is the "cold coil" that the air passes through inside the dash, freezes closed with the moist air and the air flow is stopped (at the vents inside the cab) , so no cold air and the unit is drawing horse power. Once the unit is unplugged and you drive for 30 minutes the air starts to flow, then it can be plugged in and starts to work fine, till it repeats
Would this be a code I could get from and ODB unit, it isolate the faulty part?
Is there a simple relay/sensor for this?
I could go to the dealer, but it's only hot here 2 months/year, kind of a waste..
Dave Albano
Arlington WA
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