I am new to this forum, and not sure how this works, but I have a Carrier air conditioner that has been diagnosed by my service tech as having the compressor cylinder froze up. He tried reversing the polarity of the motor to make it run backward to try free the cylinder with a gadget he had, without success
I completly trust this tech as I've been dealing with him for twenty yrs. He quoted me a price of $2500 For a new unit.
While brousing a DIY website they said some techs will move the motor back and forth to free it up, but they did not say how to do this. It looks like a sealed unit to me.