Today the A/C stopped working. Fancy that 85f outside and coming back from BJ’s.



When I got back I turned the A/C on and found that the compressor clutch was slipping every so often. I checked the pressure and temperature and that is all I have done at this time. FYI this is on my 2000 S-Type 160,000mi



The low pressure range is 32/39psi and the high pressure range is 249/252psi (only high side fluttering) and the outside temp is 82f at the time of my test. Looking at the readings they are close to normal but wanted to run it by you all to see what input I get.

 

What is the temperature of the air at the centre vent with the system on HI?

If the clutch is 'slipping', that could be an indication that the compressor is about to seize or disintegrate internally.

 

The output temp I last measured was 49/50f I did notice that every now and then I would hear a snap like a pressure relief and would notice a fluctuation in the gauges but just momentarily.

 

Gus, how did you determine the clutch was slipping?

 

I could hear and see it.

 

 

Today I did a little checking. Got the car on the lift and checked voltage to the compressor and it had a continuous 12.6v I also noticed oil leak from the compressor. On my first test I had good to fair readings on the low and high side so I would say the compressor is going south.



Link

 

Forgot to add this photo

 

Replace the compressor and add the correct amount of oil. Replace the serpentine belt if the old compressor was causing the clutch to slip.

 

Gus, that's a great video. I can safely say I've never seen a compressor clutch slip and grab like that. And judging by the leak, it looks like you're due for a new compressor anyway.

One caution about that voltage reading, however. Was that 12.6v measured with the plug disconnected? If so, there is one more quick check you should run. You see, with the plug disconnected and the circuit not under load, it's very easy for a voltmeter to be fooled. In an extreme example, say a multi-strand wire has only one teensy strand still intact. All the other strands are broken. With the circuit unloaded (plug disconnected), enough current will still flow through that single strand for the meter to show good voltage. Put the circuit under load, however, and the current flow will be severely restricted and the clutch can't develop enough clamping force, causing slippage. So even though your existing clutch is probably shot from prolonged slippage, the root cause could be restricted current flow on the control circuit. If the root cause is still present, the clutch will continue to slip on the new compressor and ruin that one too.

If the current flow is restricted, there are many possible causes, not just broken strands. You could have a bad control relay, loose fuse, loose sockets for the fuse, etc. All you need is some fault that lets a minuscule amount of current to flow to the meter, but not enough for the circuit to operate at full power under load.

Two minutes under the hood with a meter and you can rule out this possibility. See post #5 here for details of clutch coil control relay #8 in the forward power distribution box:

AC compressor clutch control circuit troubleshooting


Remove the relay and test the grip of the sockets for each of the 5 contacts. Use a thin strip of metal the same thickness as the protruding contacts on the relay. Next, with the engine off, set your meter to amperage (minimum 10A capacity) and connect the red lead to socket #3. Connect the black lead to socket #5. The clutch coil will now be energized and you should hear a clunk as the clutch engages. Your meter should show approximately 2.8 amps of current draw. That is what I measured on my '02. I'd say anything in the 2.6 - 3.0A range is good. If less, you've got either an external fault restricting current, or a bad clutch coil. If over 3.0 amps, you've probably got a partial short to ground drawing too much current. Depending on the location of the short, it's possible current is being diverted from the coil itself, once again reducing the clamping force. This test arrangement covers almost everything in the clutch coil circuit except the the relay. That's why I'd also suggest swapping the relay with a similar one from a known-good circuit, such as as the fog lamps.

Back to that leaky seal. Have you considered modifying the bypass valve on the new compressor? Details in the middle of post #4 of my troubleshooting guide linked above. It looks very simple to do.

 

When I tested the voltage it was at the lead going directly into the compressor for the clutch and when it began slipping I monitored the voltage and it was consistent. As for the modification I am just going to replace the unit and the separator and draw a vacuum and recharge and see how it goes. It worked well up to this point.

 

Replaced the A/C compressor and dryer pulled a vacuum and recharged and all is back to normal.