Automotive Air Conditioning Information Forum (Archives)

brianr134 on Sun September 18, 2011 11:25 PM

Year: 2002
Make: GMC
Model: Sierra 1500
Engine Size: 5.3L
Refrigerant Type: R134a
Ambient Temp: 65F
Country of Origin: United States

Greeting, no A/C expert here but hoping to get some advice and pointers on this.

Starting out, I have a static pressure around 60PSI. I do get cold air, temperature of air delivered has not significantly changed.

With the A/C system engaged and holding the RPM's to 1500-2000, the A/C compressor belt begins to slip after a second or two causing a chattering of the tensioner. Note: I do not get a chattering from the belt slipping when the engine is idling.

Watching the High/Low pressure sides PSI, I'm finding the following: The HPS (high pressure side) will continue to build up to 350-375PSI, where it seemed to just stop building and hold constant. My chattering begins when the HPS goes above ~200PSI. The HPS PSI does not exceed ~150PSI when the engine is at an idle, hence why I don't get a chatter at idle.

The LPS (low pressure side) begins to drop to around 30-35PSI. My LPS can not seem to reach the 20-25PSI required to interrupt the A/C request signal to disengage the compressor clutch.

Now if I remove the electrical plug from the low pressure switch and simulate the low pressure switch cycling (not at specified PSI values however), I can get the HPS and LPS pressures to fluctuate as if the LPS PSI was dropping below the 21-25PSI needed to interrupt the A/C request signal to disengage the compressor clutch.

Searching the web, I can't seem to get the right search terms to dig anything up that is relevant. They get as far as diagnostic: belt slips causing chatter; posted reply: replace A/C compressor.

From what I'm finding on the orifice tube, a clogged tube doesn't seem to be the culprit as the symptoms of that are below normal low side pressures.

Any help or ideas?

Thank you,
-Brian

chris142 on Mon September 19, 2011 11:52 PM

The chattering tensioner on these trucks is a sure sign of pending compressor failure.