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Discussion Starter #1
Compressor on my SS locked up awhile ago. Happened when I was topping up system after winter storage. So, when I was working on it last fall, I swapped out the compressor for what I thought was a good used/rebuilt one. Pulley free wheels fine, I can grab the clutch and turn over the compressor without issue. Connector is plugged in. I did new rear seals.



Vacuumed out the system (I have a pump and gauges). It pulled down to negative 30 inches, and held for a few hours without moving. Great, no leaks. Time to fill. Started car, turned on AC, connected a can and the vacuum pulled some in right away. Compressor did not start.



Double checked fuses. Disconnected the low pressure switch connector off the accumulator. Jumped it. Compressor does not start. I do hear the engine increase slightly in RPM, so I'm sure the PCM is getting the AC on command. I've never had one that DIDN'T start with the jumper wire.



Any ideas for me? Am I missing something? Or, is it just "take it apart again and throw another compressor in there"...
 

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Do you have power at the Low Pressure Switch? Jumpering only works if the switch is bad (or the pressure isn't high enough).

Do you have a couple ohms of resistance across the compressor clutch?

Is there a ground at the car side of the compressor clutch connector?
 

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I would check the clutch coil resistance at the compressor plug.



Check the compressor fuse.



Check for voltage on the car harness side.



You could remove the relay and jump the power to the compressor coil and see if it runs.


The other A/C pressure sensor goes to the PCM and may prevent the clutch from engaging.
 

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Discussion Starter #4
The car side clutch connector is showing full voltage with AC on and pressure switch connector jumped. Fuses are good, tested. Relay removed, re-seated. So it looks like everything is working as it is supposed to. Voltage goes to the compressor when required. It just won't start.


I'll check the resistance value across the compressor terminals. What should it be?
 

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Did you confirm that you have a ground as well at the car side clutch electrical connector?

The resistance across the clutch coil should be in the single digit ohms - 4, 5, 6, etc.
 

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Discussion Starter #6 (Edited)
Did you confirm that you have a ground as well at the car side clutch electrical connector?

The resistance across the clutch coil should be in the single digit ohms - 4, 5, 6, etc.

No (to first question). Just probe the connector and jump to ground to test for continuity? Does it matter which side?



Resistance across the clutch connectors was .02-4 on the 200 scale. I do get the beep if I switch it to continuity. Not sure if I'm supposed to...


Edit: back from the garage. Car off, I have continuity to ground on the car side connector. Purple wire, not green.
 

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Just so I understand - You have verified that you get 12v at the car side clutch connector and that you have a ground in the same connector, right?

4 ohms is much better than 0.02 - it should be stable. If you have a lower range for resistance measurement, you won't hurt anything by using it.

So, the next thing to try is to put the circuit under some load. Do you have a turn signal socket or similar that you can plug in to the car side connector? Something that draws a few amps instead of a few milliamps (like a test light or multimeter). You might have voltage, but without any current carrying capacity, it could all go away once connected to the coil.
 

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Discussion Starter #8
Correct, I have 12v car side connector when ac is commanded, and I have ground on that connection on the purple wire.
 

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Jay, try substituting a real load across the + and - terminals of the AC plug.

Something like an H4 or H1 halogen bulb.

Many times a LED test lamp or a meter will indicate everything is OK but the system will not carry a real load.

If it really is the compressor clutch, I do have a brand new compressor here north of the border collecting dust :)
 

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Discussion Starter #10
I'll see what I can find to create a load. I also have another super grungy used compressor that I pulled from a parts car. I will check the resistance on the connector on that one to compare.



Keep that compressor for me!
 

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If the resistance is good, use that super grungy one as your "load" Just run some jumper wires from the car connector to the grungy compressor connector so it's easy to measure voltages, verify if the clutch engages, etc.
 

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Discussion Starter #13
Couldn't resist doing more troubleshooting!



Everybody loves pics, too. Here's what I've got.


Grungy OEM parts car compressor, resistance 3.5ohms. Interestingly, pulley spins, and I can turn the compressor by hand. Should have installed this one, lol






Aftermarket/rebuilt compressor that I installed .. resistance 0.2ohms. I'll assume "not good".






It was tough to do a proper load test with the grungy one, couldn't hold the wires on both terminals while trying to rotate the pulley to check the clutch function. Did get a spark when touching the wires to terminals, though. So, I went searching, and found my bag of headlights. Car on, AC on, pressure connector jumpered, the car side connector had no problem illuminating the headlight. Low and high beam! You can see the replaced compressor here (note that different style clutch).





Are we at the point where I can say this compressor (or at least the clutch) is DOA? I don't mind doing the work over, just want to make sure that it will be worth it. On the positive side, it's still holding pressure...
 

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If the one on the car is 0.2 ohms (and stable) then it's shorted internally and can't build enough of a magnetic field to pull the clutch in. Just for fun, switch polarity and check the one on the car again - some clutches have a diode built into them which will show a "short" one way and proper resistance the other way. Maybe the aftermarket one is that way and the polarity is reversed. This is just a double extra sure check step. If you get the same 0.2 ohms with either polarity - then the clutch coil is for sure bad.

There should be a nice audible, authoritative "click" when the clutch is powered, but your lightbulb test shows that your wiring is good to carry a load so the only remaining thing is the clutch itself.

I don't know if the clutch on these are replaceable without replacing the whole compressor or not.
 

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I haven't run into a compressor yet that you couldn't replace the clutch on, it's just a matter of having enough room (which there is on these cars), occasionally having the right tool and whether you can buy a clutch by itself. I have run into a few where clutches are not sold individually. Pretty sure on these it's just the three bolts on the clutch and then some sort of puller if it doesn't come off by hand. Someone can probably confirm or correct that. Some also incorporate snap rings, not sure on these, I've done a bunch, but never the model on our cars.
 

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I haven't run into a compressor yet that you couldn't replace the clutch on, it's just a matter of having enough room..
Across the cars I've owned, if the clutch goes, the compressor nose seal is usually not far behind. The cheapest clutch for these cars is $67 on rock auto; the whole compressor is $100ish more so I just replace the whole compressor. Although, if you're trying to avoid opening the system, just doing the clutch is an option.
 
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