Cadillac Repair: 1990 Cadillac A/C System - Power to Clutch, cadillac brougham, degree air

Question
The A/C is intermittent in our 1990 Cadillac Brougham.  The AC is original - never needing repair until now.
Sometime there is cold air for half of a day, then nothing but hot air.  Yesterday the AC was not working.  The clutch was not engaged. I first checked the low pressure switch and it was closed. Next I checked the voltage at the clutch connector, with the connector disconnected from the clutch.  It measured 12 volts open circuit.  When connected to the clutch, the voltage drops as if there is not enough current to pull in the clutch. Then, I stripped a piece of insulation off the positive lead to the connector, while still connected to the clutch and momentary ran 12volts from the battery directly to the positive clutch wire. The clutch pulled in immediately AND Stayed in when I removed the external 12 volts.  I then shut off the engine and restarted it. The AC clutch pulled in fine and got plenty of 50 degree air.
I started the car 12 hours later and the AC is still working fine – What do you think the problem is? Do you have a schematic of the AC system / control board?


Answer
Hi Bill, I have a schematic but unfortuneatly I have no way of sending it to you. What I would suspect is the a/c compressor relay has high resistance across the contacts and closes when it wants to. The fact that you can make the clutch pull in immediately when jumpering it means there is resistance in that circuit and that is possably the relay. Hope that gets you cooling again. Bill