The symptoms I have are this: Some times I can be riding along and the AC is blowing nice and cold (I have measured it at 48 degrees F when it was 90 outside), and all of the sudden, instantly, I have hot air blowing out instead of cold air. And it is real hot! This morning, I had nice cold AC, but when I got to the car to go out at lunch, it would only blow HOT air, and regardless if I turn the AC on, off, hold in the AC button, etc., I cannot get it to blow cold air.
I am stumped, but I do hear the compressor come on when I push in the AC button. I replaced the monovalve a few years ago, so I don't think that is the problem, and am hoping that replacement of the button control unit will fix it.

I really appreciate all of your advice and help!

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1983 300D (Hans)