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No clutch engagement: 96 GMC K1500

jay on Sat April 12, 2008 10:51 PM User is offline

Year: 1996
Make: GMC
Model: K1500
Engine Size: 5.7
Refrigerant Type: r134a
Country of Origin: United States

Need some info on troubleshooting this truck. 96 GMC k1500

System has full refrigerant charge.
Clutch will not engage when dash button is pressed.
I ran a jumper ground to the clutch and using Powerprobe, the clutch will engage and compressor turns.

Looking at data stream on snap on scanner, when ac button is pressed,
AC request= NO
AC enabled= No
AC relay= Off

However,using the bi-directional controls, I can command the clutch on and off.

I'm in the process of reviewing wiring diagrams in alldata.
Is this most likely a control head problem?
Thanks in advance for any tips or items I need to check to point me in the right direction.


GM Tech on Sun April 13, 2008 12:20 PM User is offline

Don't you just love it when they say "refrigerant charge full" The only way you could ever state this is if you witness the full factory specified charge amount being put in the system and you are testing it immediately after. If any time has elapsed since charging, this soon becomes an unknown. You cannot tell how much is in the system by static pressures!!!

So with that in mind- and knowing that 65% of all a/c failures on the road are due to loss of charge- try jumpering the switch connector on the accumulator- does compressor engage? Don't run it very long like this if it does......

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Cussboy on Sun April 13, 2008 2:29 PM User is offline

Like GM Tech said, you need to use gauges to determine whether you really have a full charge, or even enough to enable the pressure switch to enable the compressor to engage. Explore that first before you even bother with wiring diagrams.

jay on Sun April 13, 2008 7:34 PM User is offline

How do I know it has a full charge? .. Well, I just charged it by using a mastercool accue charge II scale using 32oz from a 30oz cylinder.
Had to jump the ac clutch to get it going.

Chick on Sun April 13, 2008 8:18 PM User is offlineView users profile

did you have to jump the two wire cycling switch to do this? was the system vacuumed and charged into the vacuum? If you jump the switch as GM tech suggested and the ac came on, change the switch, if it's blowing cold that is..Pressures while running along with ambient temp will also help us help you....

Also this OBD2 system, so I don't know if a battery disconnect will work to reset codes, but it's worth a try if no power is getting to the cycling switch.. But as I stated, if you jumped the cycling switch to get it running, it sounds like a bad cycling switch, provided the full charge has been charged into vacuumed system..

Email: Chick


Freedoms just another word for nothing left to lose

Edited: Sun April 13, 2008 at 8:21 PM by Chick

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