Air conditioner blows hot and cold air

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I have seen similar things about the 190.

Mine is a 1985 500 SEL, Sometimes, blows cold air out of all 6 vents.
Other times, blows cold out the two center vents, and two lower right and left vents. But the left and right upper vents sometimes blows hot air, and through the defroster.

Recently, had the air conditioner go whacky. The compressor (has two terminals) and aux fan was not working. Mechanic said that there was no ground, and to ground either terminal to the frame from the compressor. Air started working fine. But itermittently, this problem above started. Also get frost on the outside of the windshield from cold air off the defroster.

The tubes at the base of the console, had cool air, but once I connected the console back up, no air at all flowing through the rear vent.

Today, I switched from air, to defrost (to try to clear the windshield (minor frost)), and switched back to air. When I did so, smoke or something came out the center right vent for a millisecond.

Why both temperatures at the same time out of different vents?

And id someone knows the answer to the other problems here, feel free to advise.

My question was, why did the air work fine all this timel wouldn't one of the two terminal plugs on the compressor be a ground anyway? Which leads me to think that one of the wires had a split in it?

Baffled by all this.