Ok, not a Buick but my son's `99 Malibu is having a little problem with the a/c. It blows ice cold when the compressor is running but starts to cycle on and off more as the temperature gets warmer, or rather, the longer it runs. Is there some kind of a thermal switch or something on this thing that could cause this? The Chiltons manual says nothing, only to take it to a certified a/c tech.
Its most likely going off on Low Pressure. there is a switch on the side of the receiver/dryer. when the pressure drops below 20 PSIG it cuts power to the compressor clutch. once the compressor stops pressure equalizes and switch releases till pressure drops again. to test it pull the plug on the switch and jump the terminals out compressor should run without cutting out. You may just need to add 1/2 lb R-134A
The 99 Malibu uses a V5 variable displacement compressor, so it does not cycle during operation. There is a switch that will open if the refrigerant gets too low but it is a trinary sensor that sends feedback to the PCM. DO NOT attempt to jumper the terminals on this switch, as you could easily damage the PCM. There is also a High Pressure cutout switch which cuts out the compressor if the High Side pressure is excessive. It's very likely that this is your problem, but you need to monitor the High Side pressure to know for sure. DO NOT jumper that switch, as the high side pressure can keep climbing until the compressor disintegrates internally or a line blows! (Or the relief valve opens, if equipped). Are the cooling fans running when the AC is on? They should be. There could also be a lot of debris between the condenser and radiator that is blocking airflow over the condenser and causing the High Side to be too high. This won't necessarily cause a noticeable rise in engine temp. Spray water over the condenser and see if it stops cycling. If so, there is an airflow issue with the condenser.
According to my gauges the high side is reading very low and the low side was about 28, but I'm not so sure that's not the fault of the gauges because I had the same thing happen on my wife's Jeep. If it isn't the gauges, what would a low high side reading indicate? I don't know a lot about air conditioning but it was blowing 36 degrees out the center vent yesterday so I find it hard to imagine it being low on freon. Yes, the cooling fans are both running.
It could be that you've spring a refrigerant leak and the trinary switch is causing it to cycle, but that would be an uncommon case. To properly troubleshoot a variable displacement compressor system, you need to evacuate the system and recharge it to a known, proper amount. You would then evaluate the pressures. Reading the pressures without the proper refrigerant charge doesn't tell you much on those systems.
