A/C Help

[SteveLuce]

My 1985 1/2 944 a/c has been operating erratically for a few months, turn it to cold and it runs hot, turn it to hot it runs cold, turn it back to cold and it runs hot for a few and then starts to cool.

So now on the hottest day of the year, I turn on the a/c switch and nothing, the clutch does not engage. I went to to salvage yard and purchased a replacement control unit, installed it and the same thing. The a/c has been working perfect for the last year, no gradual decline in performance. Until yesterday. I just ordered a new relay for the fuse box, it wont be here till Friday, but if someone has a clue it would be great to hear from you.

I've had a/c challenges in the past with other cars and it usually starts to perform poorly for a while then it fails, but the difference here is it was working fine one day then nothing. The big indicator of control unit failure, a/c relay, or compressor clutch problems are the fact that it just failed. Is there a sensor in the cabin that could fail? something that measures the temp of the cabin then tells the controller what to do, or is it all in the control box?
Any help is a tremendous help?

[Razorback1980]

There is a temperature control sensor, but it doesn't run the clutch of the compressor. If the compressor is not engaging, check the freon levels, then high and low pressure switches. Any of those items will prevent the clutch from engaging. After we get the compressor going, we'll check a few more things. Do you know how to check the freon and/or pressure switches? if not, let me know.

[SteveLuce]

Thanks Tom for responding.
As far as I know, the only systems that really confuse me ar the a/c system. So lets start at the beginning. If it were engine or trans related I'm your guy, but A/C totally ignorant here. Hi Lo pressure switch? Freon levels? duh!