Hi everyone, my girlfriend's got a 2000 GMC Jimmy and her AC's not working. I'm new to GMCs/Chevy's and not that good with auto repair in general!

Anyway, I was trying to check the pressure on the low side of the A/C but I'm not exactly sure I used the right valve. Where exactly is it located? The valve I used 1) didn't cause an explosion so I'm guessing it wasn't the high side! and 2) is located on what I think is the accumulator (?). There are, of course, no markings whatsoever.

So when I hooked it up the pressure fluctuated as the compressor cycled on and off from the "low range" to the "caution/danger" range. I did not remember this happening in the past when I've checked other cars.

Any help/advice you could offer would be appreciated. (I've searched this forum and the internet in general looking for a diagram/picture showing where the low side valve is with no luck!)

Thanks,
Russell

 

Yep the low side service fitting is on the accumulator and it's the smaller of the 2 fittings. The pressure should be about 30-40 PSI on the low side with the compressor clutch engauged and it should cycle the clutch off when it drops below 25 PSI.

 

System won't have a pressure differential from low to high when the compressor ain't compressing because the compressor compresses . In R-134A systems (use quick connect ports, not threaded), you can always tell which port is which by the size of the port (low is always smaller (13mm outside diam.)than the high (16mm OD) because you definitely don't want to accidentally try to charge into the high side = kaboom [sm=smiley21.gif]), or the "L" printed on them sometimes, or the position in the system. It's easiest to just remember low = small.