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AC Compressor Clutch Troubleshooting


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OldMrGrumpy
New User

Apr 1, 2014, 6:36 PM

Post #1 of 8 (3543 views)
AC Compressor Clutch Troubleshooting Sign In

The AC in my wife's GM SUV stopped working in the past day or so. I figured out the clutch was not engaging on the compressor.

I thought it might be the safety switch, so I jumpered across that, no start.

Next, fuse panel. The clutch uses a 4-pin micro relay (pins 85-86 are the pull-down/fuse, pins 87 and 30 are the switch). I ohmed out pins 85-86 and got (ironically) 85 ohms. Compared this to a new relay at the parts store and got the same reading across the same pins. Relay seems ok, but replaced it anyway.

Checked voltage at fuse panel with car running, got 13.5VDC in the slots corresponding to pins 85 and 86 on the relay.

I used a wire jumper to short between the slots for spins 87 and 30 (switch contacts) and the compressor clutch engages; AC blows cold.

Left jumper in place with AC running long enough to check freon - it's in the middle of the green range based on ambient temp.

But if I pull the jumper and replace with the new relay, clutch will not engage.

What should I check next?


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Apr 1, 2014, 6:49 PM

Post #2 of 8 (3539 views)
Re: AC Compressor Clutch Troubleshooting Sign In

Year, make, model, and engine size? Automatic or manual climate control?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Apr 1, 2014, 7:01 PM

Post #3 of 8 (3531 views)
Re: AC Compressor Clutch Troubleshooting Sign In


Quote
Left jumper in place with AC running long enough to check freon - it's in the middle of the green range based on ambient temp.


If you're using one of those DIY kits, you're wasting your time. You need a full set of high and low gauges.

There are any number of reasons for the PCM not to energize the relay.

I would have given you a wiring diagram but you didn't bother to list year, make and model.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



OldMrGrumpy
New User

Apr 1, 2014, 7:07 PM

Post #4 of 8 (3524 views)
Re: AC Compressor Clutch Troubleshooting Sign In


In Reply To
Year, make, model, and engine size? Automatic or manual climate control?


2007 Saab 9-7x 5.3L V-8 Climate control


Discretesignals
Ultimate Carjunky / Moderator
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Apr 1, 2014, 7:54 PM

Post #5 of 8 (3512 views)
Re: AC Compressor Clutch Troubleshooting Sign In

Your going to need scan tool data and some bidirectional control. Which means, you'll probably need to bring it to a repair shop.

The powertrain control computer operates the AC clutch relay. The command to the PCM for the AC request is given by the AC controller. The high side pressure transducer is monitored by the PCM and the low side pressure switch is monitored by the AC controller.

You don't want to be shorting the high pressure transducer. It is not a switch, but a sensor that monitors actual pressure.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Hammer Time
Ultimate Carjunky / Moderator
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Apr 2, 2014, 2:32 AM

Post #6 of 8 (3497 views)
Re: AC Compressor Clutch Troubleshooting Sign In

Be very careful where you go poking around in this system. You can fry a module in a heartbeat.



Serial data diagram





Compressor controls






~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



OldMrGrumpy
New User

Apr 2, 2014, 5:35 AM

Post #7 of 8 (3491 views)
Re: AC Compressor Clutch Troubleshooting Sign In

I'll check the other fuses in this diagram for continutiy, and if nothing is found, I'll take it to the shop


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Apr 2, 2014, 5:54 AM

Post #8 of 8 (3489 views)
Re: AC Compressor Clutch Troubleshooting Sign In

Good plan



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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