Let me start by saying I consider myself very mechanically inclined and have a mountain of DIY experience working in a wide variety of vehicles’ various systems. One such system that I’ve always struggled with, however, has been A/C. I find myself the proud owner of yet another vehicle without working A/C so I’ve decided to ask for help this time.
What I know: When I got the Envoy, it did not have working A/C so I put a guage to the low side and saw it had no pressure. I figured that would explain why the compressor wasn’t engaging - when the system gets too low on refrigerant, the computer will keep the compressor from running because the compressor requires the oil thats in the refrigerant to keep itself working properly. No refrigerant = no oil. Since the system had emptied I figured i should see if it would hold a vaccum, so I vaccumed it to -30 in Hg for abt 15 min and let it sit in a closed state without the vac running for an hour to see if it had a substantial leak anywhere. It held the vaccum so I moved on to the recharge. The spec for my vehicle said it wanted 3lbs of refrigerant so i went and bought 4x 12oz bottles and hooked them up 1 at a time. I added the first bottle with the car off since the compressor was in lockout anyway and that took about an hour and a half. After that, I turned the car on and the compressor started to engage so i figured I was on the right track. 2 bottles of refrigerant later and I had cold A/C! I decided to take the car for a quick drive before adding the 4th bottle. When I got back from that drive around the block, the A/C suddenly stopped working and my car had started stuttering at idle in regular intervals. Upon closer inspection, I noticed that it was stuttering as it tried to engage the A/C compressor, but would quickly give up and return to normal, repeating roughly every 4 or 5 seconds. I thought, well maybe 3 cans wasnt enough afterall, so i guess i’ll add that 4th one now. I hook the guage back up to the low side to find that it now reads over 120 psi!! I had always understand that you’re supposed to fill an A/C system by weight, not by pressure, so I hooked up the 4th bottle but of course… the pressure in the system was far too high and it wouldnt accept any more.
After a fair amount of poking around on google, I found that my stuttering compressor symtoms were consistent with over-filling a system, so I decided to release some of the refrigerant IN A TOTALLY SAFE AND LEGAL MANOR until the compressor stopped stuttering. Unfortunately, that wasnt until around ~20psi, by which point it had gone back into low pressure lockout and still just didnt work at all. It seems like no matter what advice I follow for this proceedure, It never works. What am I doing wrong?