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No Cooling Due To Compressor Disengage Safety

RedReattaRuss on Mon June 08, 2009 12:50 AM User is offline

Year: 1991
Make: Buick
Model: Reatta
Engine Size: 3.8
Refrigerant Type: R12
Ambient Temp: 55
Pressure Low: Vacuum
Pressure High: 100
Country of Origin: United States

My 1991 Reatta uses the orifice tube type expansion valve with cycling of the compressor clutch for prevention of freeze up. GM calls it CCOT, Cycling Clutch Orifice Tube, controlled by the BCM, Body Control Module.

The car has had little use in 18 years, and has illuminated the "Low Refrigerant" dash lamp for several years. Upon AC request, the compressor would cycle on three times for a second or so each time, then lock out. The system showed no refrigerant, so I evacuated for half an hour, then added 12 oz. of R12. Upon testing, the compressor would cycle several times, then lock out on error. I removed the AC relay and carefully jumpered the relay contacts with a wire; one second on, three seconds off. Each time I energized the clutch the low side pressure would go from the ambient pressure of 50# to a vacuum, whereas the high side pressure never went over 100#. This placed a severe strain on the engine, which almost died.

Is the orifice tube plugged? Seems there's a blockage somewhere. Thanks. Russ

mk378 on Mon June 08, 2009 9:43 AM User is offline

This sounds normal; you only have 12 oz of refrigerant in it which is a severe undercharge. Undercharged, the compressor will make short cycles, and when the computer detects several short cycles in a row it will "lock out" the compressor from running any more. You should be able to clear the lock out by disconnecting the car battery (with engine off) to reset the computer.

Since you were jumping the relay, the computer did not know the compressor was on, so it didn't compensate by increasing the idle air. Thus the engine slows down abnormally.

As you found the pressure at zero there is most likely a substantial leak though.

GM Tech on Mon June 08, 2009 10:51 AM User is offline

I agree with all the above- put the right amount of refrigerant in it after a good long vacuum and report pressures.....don't stop at 12 ounces....

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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......

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