My wife recently got a terrific deal on a mint '98 Lumina, which she purchased at an auction for her company's older cars ($625!!). The car has high mileage (138k), but it looks and runs GREAT.
Last week she complained that her a/c had started to blow warm air. Upon checking it out, I noticed that the compressor clutch was not engaging. I thought it might be due to low coolant level, so I checked it at the low-side port with an a/c pressure gauge: it read 44psi, which I believe is just about what it's supposed to be @ full charge. So I assumed an actual low coolant level wasn't the prob.
Next, thinking it might be a defective pressure switch which was incorrectly "telling" the compressor clutch that the coolant pressure was too low, I attempted to "jump" any 2 of the 3 wires together to see if I could effectively bypass the switch and "fool" the compressor into engaging. No go. Of course, I didn't have a wiring diagram, so I was really just shooting in the dark here.
After checking all the involved electrical connections for continuity, checking the compressor fuse, swapping the compressor relay for the identical fuel pump relay, and a bunch of wire-jiggling and other general mucking about, I finally gave up on getting the compressor to engage. I put everything back together, and then went inside for a well-deserved Corona w/lime.
OF course, later when I started the car to move it outta my work area, the compressor started to engage and dis-engage correctly as I worked the interior AC controls - although it was still only blowing hot air. Now with the compressor running, I checked the low-side pressure again, and this time it read only around 24psi.
At that point, I decided to take a $6 chance & try adding a can of R-134a. The system took the whole can, and the pressure now read 44psi with the compressor running. Gradually, the system started blowing (somewhat) cold air.
I thought I was outta the woods, but after using the car for a few days in 95 degree/105% humidity weather, my wife tells me that the a/c isn't NEARLY as cold as it used to be - she says now needs to have it on MaxA/C, fan=4 to cool things off. On checking it out, I had to agree with her: it's pretty lame.
Any suggestions? Should I bleed and/or purge the system entirely and then add 3 new cans of R134a? Would any of those additives that I've seen (ArcticFreeze, MaxiFreeze, link below)work to lower the cooling point, given that it's a hi-mileage car with a hi-mileage compressor and evaporator?
JohnB