Replaced AC compressor, will not engage - Chevy Impala SS Forum
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post #1 of 16 (permalink) Old 07-08-2019, 03:15 PM Thread Starter
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Replaced AC compressor, will not engage

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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post #2 of 16 (permalink) Old 07-08-2019, 06:10 PM
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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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post #3 of 16 (permalink) Old 07-08-2019, 06:25 PM
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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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post #4 of 16 (permalink) Old 07-08-2019, 07:22 PM Thread Starter
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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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post #5 of 16 (permalink) Old 07-08-2019, 08:30 PM
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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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post #6 of 16 (permalink) Old 07-08-2019, 09:00 PM Thread Starter
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Quote:
Originally Posted by Fix Until Broke View Post
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.

Last edited by jayoldschool; 07-08-2019 at 09:10 PM.
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post #7 of 16 (permalink) Old 07-08-2019, 11:21 PM
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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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post #8 of 16 (permalink) Old 07-09-2019, 08:28 AM Thread Starter
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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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post #9 of 16 (permalink) Old 07-09-2019, 07:57 PM
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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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post #10 of 16 (permalink) Old 07-10-2019, 11:29 AM Thread Starter
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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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