Help! AC clutch not engaging?
10-14-2014, 05:44 AM
#1
Its 110 degrees here (no joke!) and AC just suddenly decided to quit on me at noon when the sun was at its mightiest and I was stuck in traffic.
Upon investigation I found that the AC clutch is not engaging. Switch the AC button on/off, the switch lights accordingly but compressor doesn't engage. Gas is full so its not due to low pressure. And the relay is good.
Got a test light to check the relay pins and discovered that there was no ground signal.
So when I jumped(?) ground buy connecting a wire from AC compressor ground at the relay to battery ground post, the clutch engaged and AC started working normally.
Any idea what my problem is?
Upon investigation I found that the AC clutch is not engaging. Switch the AC button on/off, the switch lights accordingly but compressor doesn't engage. Gas is full so its not due to low pressure. And the relay is good.
Got a test light to check the relay pins and discovered that there was no ground signal.
So when I jumped(?) ground buy connecting a wire from AC compressor ground at the relay to battery ground post, the clutch engaged and AC started working normally.
Any idea what my problem is?
Last edited by Freefallin; 10-14-2014 at 10:56 PM.
10-14-2014, 07:34 AM
#2
You didn't say what year/model you are working on so I just picked 2000 Trans Am as representative (Camaro should be the same and I doubt there's much difference between years).
The A/C compressor ground has nothing special in the way of switches or sensors - it just runs straight to ground G112 on the rear of the left cylinder head. You should check that the ground point is clean and tight and confirm that the wire between the compressor and the ground is undamaged.
Although you can always patch in your own ground wire, the factory wire has other circuits spliced into it so I would not remove it without checking those first - you could end up with other circuits suddenly not working.
The A/C compressor ground has nothing special in the way of switches or sensors - it just runs straight to ground G112 on the rear of the left cylinder head. You should check that the ground point is clean and tight and confirm that the wire between the compressor and the ground is undamaged.
Although you can always patch in your own ground wire, the factory wire has other circuits spliced into it so I would not remove it without checking those first - you could end up with other circuits suddenly not working.
10-14-2014, 08:17 AM
#3
You didn't say what year/model you are working on so I just picked 2000 Trans Am as representative (Camaro should be the same and I doubt there's much difference between years).
The A/C compressor ground has nothing special in the way of switches or sensors - it just runs straight to ground G112 on the rear of the left cylinder head. You should check that the ground point is clean and tight and confirm that the wire between the compressor and the ground is undamaged.
Although you can always patch in your own ground wire, the factory wire has other circuits spliced into it so I would not remove it without checking those first - you could end up with other circuits suddenly not working.
The A/C compressor ground has nothing special in the way of switches or sensors - it just runs straight to ground G112 on the rear of the left cylinder head. You should check that the ground point is clean and tight and confirm that the wire between the compressor and the ground is undamaged.
Although you can always patch in your own ground wire, the factory wire has other circuits spliced into it so I would not remove it without checking those first - you could end up with other circuits suddenly not working.
Also I meant ground at the relay (fuse box) not getting signal. I'm not sure if you were talking about that or the ground wire at the compressor. Or is it all the same :-/
Last edited by Freefallin; 10-14-2014 at 08:24 AM.
10-15-2014, 07:00 AM
#4
I don't have GTO schematics so I can't be very specific, but in general the compressor relay coil gets power from an ignition-switched fuse and has a ground that is controlled by the PCM/ECM. Substituting your own ground there will make the A/C run but not cycle on and off so you could cause more serious problems. Unless you have a scan tool to check for codes from the PCM, I recommend you get a shop to look at it.
10-16-2014, 12:26 AM
#5
I don't have GTO schematics so I can't be very specific, but in general the compressor relay coil gets power from an ignition-switched fuse and has a ground that is controlled by the PCM/ECM. Substituting your own ground there will make the A/C run but not cycle on and off so you could cause more serious problems. Unless you have a scan tool to check for codes from the PCM, I recommend you get a shop to look at it.
10-17-2014, 12:38 AM
#7
Makes perfect sense however its a pretty distinct clear click noise accompanied by an rpm change when the compressor kicks in. So if the compressor was turning off or on, I wouldve easily heard/felt it. You sure its not different with the gto? Perhaps a different system where cycling is not required?
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10-17-2014, 01:18 AM
#8
Here is the the schematic. Could someone that is electronically inclined help me figure out what my problem is? Obviously I have no idea how to interpret the diagrams. Fast learner thou!
10-17-2014, 06:41 AM
#9
Makes perfect sense however its a pretty distinct clear click noise accompanied by an rpm change when the compressor kicks in. So if the compressor was turning off or on, I wouldve easily heard/felt it. You sure its not different with the gto? Perhaps a different system where cycling is not required?
10-17-2014, 07:17 AM
#10
You can see in the first schematic that the ground for the relay coil is connected to the PCM "AC Clutch Relay Control" on pin 43. The PCM enables and disables the clutch by closing and opening the ground on that pin which allows the relay to engage and disengage thus controlling power to the A/C clutch.
If you have a multimeter, you can test the circuit at the relay socket in the underhood fuse block. Unplug the relay and test for ground on the light green with black wire when the engine is running. You should see the ground come and go as you switch the A/C on and off. If not, either the wire to the PCM is damaged or the PCM is not switching properly. Fixing the wire is no big deal but if the PCM is not switching then you really need a pro to check it because it could be anything from a bad pressure sensor to a bad PCM (very expensive but not likely).
Interesting schematics you found - they're from Holden Australia and may not be exactly the same for domestic US models. They use the correct ISO chassis ground symbol that looks like an E on its side. Here in North America, it is common to use the earth ground symbol (a set of horizontal lines forming an upside down pyramid) for all grounds even though there is no actual connection to earth in a car. Trivial but interesting.
If you have a multimeter, you can test the circuit at the relay socket in the underhood fuse block. Unplug the relay and test for ground on the light green with black wire when the engine is running. You should see the ground come and go as you switch the A/C on and off. If not, either the wire to the PCM is damaged or the PCM is not switching properly. Fixing the wire is no big deal but if the PCM is not switching then you really need a pro to check it because it could be anything from a bad pressure sensor to a bad PCM (very expensive but not likely).
Interesting schematics you found - they're from Holden Australia and may not be exactly the same for domestic US models. They use the correct ISO chassis ground symbol that looks like an E on its side. Here in North America, it is common to use the earth ground symbol (a set of horizontal lines forming an upside down pyramid) for all grounds even though there is no actual connection to earth in a car. Trivial but interesting.