Compressor keeps running after thermostat is turned off.

check and test compressor relay and circuit

If the contactor relay by your compressor does not open the compressor will stay running. Either the contactor is at fault for staying stuck OR the thermostat continues to send out the 24 volts to activate the contactor and keep compressor running

On the circuit board there is a micro relay that is stuck in the closed position. Or it is wired so that the sensing ability (thermostat) controls the comp and it is stuck closed

I would change the thermostat. Sounds like a bad thermostat.

If the compressor keeps running, just turn the thermostat down until it stops.

Sounds like the contactor is stuck. Turn the power off on both units and remove panel on condenser. Pull out on the contactor if engaged. Likely still needs replaced, it's going to happen again.

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If its doing it over night or in several hours, you need to check the thermostat. Turn it all the way to the warmest setting and listen for the compressor to shut off. If the compressor keeps running at the warmest position your thermostat is shorted. If you do hear your compressor shut off , and the thermostat is working, you are probably low on refrigerant.

Some possible problems..turn thermostat where AC compressor should not run. measure lo voltage to the contactor in the compressor housing. If there is voltage there then thermostat is defective. Remove one lead of lo voltage at contactor. Compresor should stop. If not contacts are stuck. Replace or burnish contacts..

Dear jack289,
The thermostat is not working properly. When thermostat cutsoff the compressor Please turn the thermostat knob to higher setting if compressor starts working then please change the thermostat. The fan will run continuously since only the compressor is controlled by the themostat.
Regards,
ramesh22

Replacing the thermostat should correct the problem. Be sure to install the thermstat exactly as the one you are removing, assuming it hasn't been changed prior. Hope this helps