How to Be Sure Compressor Needs Replacing?

[tntv]

So my AC does not work. I do not see or hear the compressor go on or the clutch engage. Seems all is dead. Fan works fine. I put a guage on the system and it registered high/danger which tells me it is either an electrical problem or compressor/clutch. I've checked the fuses and all are fine. Can I just assume it is the compressor and go buy a new one and have someone put it in? Thanks for any advice! 2000 Astro

[chevymaher]

So my AC does not work. I do not see or hear the compressor go on or the clutch engage. Seems all is dead. Fan works fine. I put a guage on the system and it registered high/danger which tells me it is either an electrical problem or compressor/clutch. I've checked the fuses and all are fine. Can I just assume it is the compressor and go buy a new one and have someone put it in? Thanks for any advice! 2000 Astro

No I would not get a compressor.It is not leaking it is probably fine.The high pressure is probably kicking the high pressure switch keeping it from engaging the clutch.2 things can cause this.A build up of acids and moisture in system.A recovery and recharge fixes that.I had the same problem with a customers car recently.It was the thermal expansion valve was stuck open.The van has a orifice tube which does that job.They dont usually go bad but I have seen stranger things.Bleed off pressure till it in safe zone see if it kicks the compressor on.If pressure shoots back up and turns it off.I would suspect orifice tube.We did a recovery and recharge on his and it worked about an hour.Replaced valve problem solved.Once pressure lowered to safe.If it kicks on and stays running. A recovery and recharge would be next step.If lowering pressure does not kick it on I would have the switch itself chacked.I know alot of ifs and maybes but at least a direction to start searching.

[tntv]

Glad I asked...sounds like a much cheaper way to diagnose with possible remedy. Thanks!!

[kennyj]

Just to add to what chevymaher said, it occurred to me that if the compressor isn't running, the pressure you are reading on your gauge is static pressure, which on the low pressure side could be quite a bit higher than with the system running. I believe a rough rule of thumb is static pressure should be similar to outside temp readings, ie. 85 lbs static pressure on an 85 degree F day.
I would look for an electrical cause for the compressor clutch not kicking in.

[redfury]

Yeah, you want to read the low and high side of the system, at a rest the pressure stabilizes throughout the entire system. Meaning, that if you see 150lbs on the low side and 150lbs on the high side without the AC compressor engaged, that would be normal. Once you kick the AC compressor over and start cycling coolant, the high side is going to be upwards 300psi and the low side is going to be around 45psi, which is why you always charge into the low side port with the engine running, AC ON.

You can usually check compressor operation by jumping the pressure switch.

[flores5996]

You might want to start checking for power from fuse to climate control switch then from climate switch to pressure switch. Then pressure switch to compressor. Oh don't forget relay if you have one.

[throrope]

I'm with all who suggest electric side and not compressor. Since it doesn't do anything, I'd be surprised if you had enough refrigerant in the system to kick in the high pressure system at rest. The low pressure switch will prevent the compressor from engaging if too low from a leak or similar and is used to cycle the system. I'd check every switch and connection systematically and specifically look for power to the clutch.

[Phantom]

Have you tried jumping the terminals on the pressure switch ? that should trigger the voltage to complete the circuit to find out if the compressor is getting voltage power to it. There is an A/C enable relay in the fuse box next to the battery, check the diodes in that fuse box and the other circuit related fuses.