My AC compressor finally gave out. I replaced it with a used one with a new magnetic clutch. I took it to an AC shop to evacuate and charge the system. They told me no power is going to the compressor. They think the compressor is bad. My understanding is the only power going to the compressor is power to engage the clutch. They said there is power to it but when the AC switch is turned on it goes off. That makes no sense to me since it was working fine before I changed the compressor. I replaced the expansion valve and the drier too.

I only see one wire going to the clutch and no other wires connected to the compressor. Could it be a bad AC switch on my dashboard? Should I just bite the bullet and install an RX8 compressor and condenser? I cannot drive the FD in summer without AC. What do you guys think? I have had this car for 25 years with a problem but that is the last moving part I had not replaced.

 

Who physically installed the used compressor with the new mag clutch? Not trying to be a douche or anything, just need to be clear on exactly what was done to help figure out your next steps. Normally, the summarized order of steps for an A/C compressor remove & replace job goes like this:

1. Evacuate refrigerant gas from system
2. Mechanical steps to physically remove & replace the compressor.
3. Vacuum the system down to at least 29~30 in/Hg, and verify that vacuum holds for at least an hour. (this is to verify nothing is leaking BEFORE recharging)
4. Recharge the system with refrigerant, test operation.

If your A/C was working fine before the old compressor crapped out, I agree with you that it's unlikely that anything is wrong with the electrical parts of the system. However, if the shop did a shoddy job - especially if they cut corners on step #3 above, it's possible they recharged it with a small leak present - this would have allowed them to charge the system, and it would have worked OK, at least for a short time before handing the car back to you. But by the time you tried to run your A/C, enough refrigerant would have leaked out to cause the pressure switch to cut off current flow to the compressor - this prevents your compressor from self-destructing, so it's "normal" operation.

To verify this theory, here's the procedure.
1. Disconnect the one pin plug from the compressor, connect it to the positive (+) lead on your voltmeter, and the negative VM lead (-) to the negative battery terminal.
2. Switch on the ignition, turn on the A/C switch & fan blower switch (any fan speed will do), and check your VM reading. If you see 12V, the electrical system is working as it should, you've got enough refrigerant in the system (at least enough to keep the pressure switch from opening) and that new AC clutch should be engaging to run the compressor. If that's the case, you got a bad compressor clutch. If you don't see 12V, go on to step 3.
3. Find the A/C pressure switch, disconnect its 2 pin connector, and put a jumper wire across its 2 terminals to bypass the switch. Do you see 12V on the VM now? If YES, then it's likely that enough refrigerant leaked out causing the pressure switch to break the clutch circuit. If that's the case, the shop that evacuated & charged the system failed to check for leaks before recharging.

 

I was the one who installed the used compressor with a new pulley and magnetic clutch. I took it to the car shop to do the evacuation and charging of the coolant gas (R134A). The vacuumed it and recharged the system successfully. I will test the voltage on the switch tomorrow. The shop said they jumped 12V to the compressor and it engaged but was not sounding good. So now I am shopping for a new compressor.

 

Do you have a Power FC? My power FC was turning off the compressor. Shop thought the compressor was cooked.

There is a glitch in the Power FC in regard to running the A/C.

There is some sort of hack to bypass the ecu and get the a/c running consistently.

 

Ok, then it probably leaked out enough R134 for the pressure switch to do it's thing and cut off power to the compressor clutch. When they jumped power to the compressor to make it run, it wasn't sounding good because there wasn't enough R134 in the system to circulate lube - by doing so they risked killed your compressor. Did the shop hook up a set of A/C manifold gauges to the system to check static pressures first before doing anything else? That's the first thing they should have done, to determine if there's enough refrigerant in the system for it to be safe to proceed with testing the compressor by bypassing its electrical controls.

 

Yes, I do have a Power FC but the AC was running fine before the compressor died. So I should not think the ECU is interfering with the operation of this compressor.

Pete, thanks for you input. Yes, the shop pulled the vacuum and checked for any leaks using a vacuum pump and manifold guages. There were no leaks. And they successfully charged the system with 2 lbs. of R134a. The magnetic clutch and pulley are both new but the compressor is not. So it may be a bad compressor. I will check the voltage with the fans on as you suggested. If that is good, then I may need to just buy a new compressor instead of getting these used ones.

 

Basic operation:
In most older AC systems like ours, engine running with the AC off, you can see the pulley rotating but the compressor shaft not rotating. When the AC is switched on (12V applied) the compressor shaft should magnetically engage with the pulley and you should see its shaft begin rotating, plus the compressor making some noise if it's working. If the compressor shaft starts rotating, but there is no noise or cooling happening, the compressor may, indeed, be defective, or some other part/sensor in the system has died. If it doesn't start rotating with AC switched on (12V applied), the clutch is bad.

As mentioned below, the inside blower fan needs to be on for that test to work.

 

Just use a power probe and put 12v (or a ground whatever the system needs for it to operate) to the A/C compressor clutch with the indoor blower motor running and see if the compressor is working properly or at least engages. That will rule out if the compressor or clutch is bad.

 

It seems some units will run with the Power FC, or will cut out a different fan speeds. So it is worth considering that Power FC may have something to do with it.

It seems to be a common enough issue that there are threads related to the problem.

 

Thanks guys for all your suggestions. I solved the problem! I tested the lead as Pete suggested to the compressor with the ignition on, the fans and AC button pressed without the engine running. There was no power coming through the lead as the shop told me. I jumped power from the battery after starting the car and the magnetic clutch engaged and the AC was running. So, I was thinking maybe my wiring harness had a problem like the shop suggested. I decided the check the relays and fuses first and I noticed the fuse under the hood was lit up. I use fuses the light up when they are blown. I replaced the fuse and reconnected the wiring harness and lo and behold everything works!

It seems every time I decide not to do everything myself, the car shops just do not have the knowledge to work on our cars. The forum is a lifesaver for me many times! This shop was telling me I had a wiring problem behind the dashboard and that my radiator fans were not going on. None of which was true! So now I have a brand new compressor on the way that I don't need. I guess I'll just hang on to is since they are so difficult to source these days like so many parts on our cars.