LB7: Intermittent AC

[lutzjk913]

Is the clutch still engaged when the ac stops blowing cold?
When you say pressures are good what are they idle and under light acceleration?
When the blend door deal goes bad the compressor still stays on
Was the compressor a acdelco or parts store?
Did he replace the accumulator and orfice when he did the compressor?

Clutch does not stay engaged.

I forget the exact numbers on the pressure.

Not sure on brand of compressor. It was used off of a old motor he had there.

And no. He didn’t replace either of those.

 

[dndj]

From the FSM

Here's what the 2003 GM FSM says, may be helpful for debugging.

The following conditions must be met in order for the A/C compressor clutch to turn on:

1. The ambient air temp is above 40F
2. The A/C low pressure switch signal is grounded (switch on the accumulator. Low side below about 25-28psi opens the switch.)
3. The A/C refrigerant pressure must be less than 429psi (high pressure 3 wire transducer on the line above the compressor)
4. The ECM receives an A/C request from the HVAC control module
5. The engine coolant temp is less than 250F
6. The engine RPM is more than 550rpm
7. The throttle position is less than 100%

A Tech2 will show realtime status of all of these inputs except the high pressure switch, as others have mentioned. Once all these potential causes have been eliminated, then it's likely related to the compressor clutch wiring, or the compressor clutch itself. Remember there is a relay in the path from the A/C compressor fuse to the compressor, the ECM controls this relay. Easiest way to eliminate the A/C compressor relay is to just temporarily swap it with another known good relay in your fuse box.

Since you have already replaced the A/C compressor and presumably the clutch as well, I guess that's ruled out already.

Let me know if you want me to post up the A/C controls schematic if you want to start verifying the wiring.

 

[lutzjk913]

Truck got dropped off last night to the shop again

Waiting to hear back.

 

[lutzjk913]

Tech found 2 loose wires in the main plug on the back of the control head.

Seems to be working great now.

 

[dndj]

Tech found 2 loose wires in the main plug on the back of the control head.

Seems to be working great now.

Good deal. Thanks for posting the fix, so much more useful informatoin for people who may be experiencing similar problems can know the ultimate resolution. :thumb:

 

[1TRIKHD]

Hopefully those loose connections were the problem Joe.

 

[lutzjk913]

Good deal. Thanks for posting the fix, so much more useful informatoin for people who may be experiencing similar problems can know the ultimate resolution. :thumb:

I searched high and low on it and replaced what I thought was bad but ultimately threw the towel in on it. I knew it was electrical but I hate wiring.

Hopefully those loose connections were the problem Joe.

Me too russ