Can't get A/C compressor to turn on.

[ruston]

Car: 1993 Audi 90
I'm trying to recharge my car's A/C and I can't get the compressor to turn on at all, not even once has it turned on. I have tried jumping both the high pressure switch and the A/C relay while the engine was running and got nothing. I'm pretty sure the compressor is not locked up. I was able to turn the A/C compressor by hand with the serp belt off, but I don't know if that would tell me anything. On the climate control panel inside the car I am unable to turn the A/C on, when I press the button it lights up but then goes away when lift off the button. I have added refrigerant and also PAG oil but still can not get the compressor to engage. If I'm not mistaken, jumping the A/C relay should bypass all of the switches and sensors and force the compressor to run, or am I missing something?

 

[Skippy722]

When you spun the compressor by hand did you actually spin the compressor or just the pulley? It’s kind of sounding like the clutch failed.

 

[Lubener]

You need to evacuate and purge the system with a vacuum pump prior to refilling with refridgerant. That would also tell you if the system can hold a charge without leaking out.I would have also replaced the accumulator too.You are attempting to add to a system that is full of air and moisture. My guess is the clutch is not engaging to the system being very low on refridgerant. What you are attempting to do can damage the system.

 

[mk378]

Is the clutch circuit intact? You should measure 3 or 4 ohms through the compressor from the clutch wire to ground. If you jump the clutch wire to battery + (ENGINE NOT RUNNING) the plate should snap in. If that works check the fuses and control system, you will likely need a schematic of the car. If it doesn't snap in when connected to the battery, press on the plate (ENGINE NOT RUNNING) and if that makes it snap in the air gap is too wide.

Very important not to jump the compressor with the engine running. This can create an overpressure. Proper charging can be done without jumping or modifying any or the wiring.

 

[Chris142]

Are you getting 12v to the coil?

 

[CleanSump]

Jump straight to the clutch and see if it clicks. Then do this running and see if the compressor itself runs, not just the pulley.
Could be a bad pressure switch that won't let it turn on. If it's broken pressure in the system won't close the circuit.
Also, is there a separate fuse for it inline in the engine compartment?