Intermittent A/C!

[crazyd]

Hey all, 

'92 GTP

Been fighting this one all summer and I'm throwing up the white flag to see if anyone else has any ideas.

A/C seems to work the first time I drive the car for the day.  Next time, nothing.  Clutch is not engaging. 

When it runs, I have 40psi at 75° on the low side and 45° at the vents.  When it shuts off, 75psi static on the low side at 75°.  Far as I'm concerned the pressure is fine. 

I have replaced the relay and the pressure switch, but neither has resolved it.

Another heat wave here in the PNW so trying to fix it.  Any suggestions?

[Black92GS]

I'm going to venture a guess that you're dealing with a failing clutch. I've seen them where the air gap becomes too great, and the clutch will no longer cycle on as expected. It's likely borderline to begin with, and getting heat soaked from the engine bay is enough to cause it not to kick on until it cools back down. 

The next time it acts up, check for a couple different things.  When you switch the AC on, the cooling fans should kick on and the idle should come up.  If that occurs, then the PCM is commanding the compressor on.  If the compressor isn't running at that point,  lightly tap the compressor clutch plate with a screwdriver, being ready for it to kick on suddenly. You'd have to do it either through the passenger side wheel well, or from under the car. If it kicks on when you tap it....it's the clutch. 

 

[crazyd]

Wow, great idea.  I had a feeling it might possibly be something heat-related because of the symptoms, but couldn't figure out what.  It's a fairly new compressor as I replaced it in 2018 with a reman from Autozone, but hey I guess you can't assume anything with these.

Edited Friday at 08:44 PM by crazyd

[crazyd]

Revs came up, fans did not activate, clutch would not engage with repeated tapping. 

New Denso compressor from Amazon, replaced in 2021.

Edited Friday at 09:17 PM by crazyd

[Black92GS]

57 minutes ago, crazyd said:

Revs came up, fans did not activate, clutch would not engage with repeated tapping. 

New Denso compressor from Amazon, replaced in 2021.

Fans not coming on may be something else…but the revs coming up tells me that everything is seen as good by the PCM and its kicking the compressor on. 
 

The clutch is 12 volts. I’d check with a test light to make sure you have power and ground at the compressor when the ac is being commanded on. If that checks out, you’re still likely looking at the clutch or the coil being the issue. If there’s something missing…then you’ll have to work back from there. 
 

 

[crazyd]

Checked it this morning after an overnight cooldown. No power at the compressor at all in MAX mode. IGN Fuse tests OK.

[Black92GS]

This is for a 92 Regal so the wiring colours may vary, but the idea will be the same. You first perform test A to determine where to go from there.  

From what I can see, all of the pressure switches, the AC request from the HVAC and such all go through the ECM, and the ECM is what controls the relay, and ultimately the Compressor. The revs coming up when you turn the AC on makes me believe the ECM is receiving all of the necessary inputs and is actively trying to command the AC compressor on through the relay….and that your issue is going to lie in that area of the system.