Engine Size: 5.7L
Refrigerant Type: R134a
Ambient Temp: 82
Country of Origin: United States
My truck's AC compressor will not turn off or cycle even if the controls are turned off.
What I know...
1. The relay has been replaced by a known good relay.
2. The system was recently charged with 2 12oz cans.
3. If I disconnect the HVAC control unit the compressor still runs.
Please help me diagnose and suggest the proper tools to buy. :-)
Aloha from Maui
Must have been hot-wired by someone-- pull the relay and or fuse in underhead fuse box to see if that disables it and help you diagnose it. If relay is wrong one- or wrong style it maybe crossing up the circuit somehow.
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......
Does it disengage if you stop the engine but leave the key on? If it does, the PCM has control of the relay OK, but something on the input side of the PCM is telling it to stay on.
Is the clutch gap nonexistant?
Crazy interference fit GM has been using for sometime now that holds on the compressor clutch plate, plate can either creep in or out, sounds like yours crept in. Should be a 20 mil gap between the idler pulley and the clutch plate. Need a special tool to adjust it.
Its a puller/installer tool, if that isn't bad enough, GM keeps on changing the design of this tool, so far have three of them. I hear Autozone loans them out, but never needed to do that.
Your not the only one with this problem, join about a million more.
To check for mechanical problems with the clutch, simply unplug clutch wire and see if the compressor disengages. I think this is going to be a basic CCOT which cycles on a low pressure switch on the accumulator, but would need to see a schematic to be sure.
Edited: Fri April 20, 2012 at 11:58 AM by mk378
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