A/C recharge help needed!

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?

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Where should I start?

When you pull a vacuum on an AC system, you should wait an hour to determine if there are any leaks, and how large.

You need manifold gauges to monitor both the low and high sides when recharging an AC system.

You must purge the air from hose from the refrigerant container to the manifold gauges before recharging the system

You must monitor the outlet duct temperature when recharging an AC system

The engine must be idling @2000 RPM’s when recharging an AC system.

There should be a large fan blowing at the condenser when recharging an AC system.

You must make correction factors to the pressures on the gauge set relative to the ambient temperture.

Now all this only applies if the AC system is totally functional.


Testers post makes me think that this is not a do it yourself repair.

You probably need to replace the receiver dryer, too. Take it to an a/c shop, this is one system I always leave to the pros.

The post makes me wonder how many shops are equipped and trained to do all of this.

You must be certified to service/repair AC systems.


It’s possible that the low side pressure switch is acting up. Along with a dozen other possibilities.

While not widely known, some of those low pressure switches are adjustable. The tiny screw is buried in the switch and requires a jeweler’s screwdriver for adjustment. Whether your Envoy is like this I have no idea.

One thing for sure. That 120 PSI on the low side will never work assuming that’s the pressure with the compressor clutch engaged. You should see 40ish or so on the low side and 250 or so on the high side.

If you’re having trouble getting the refrigerant to leave the can boil a pan of water and drop the can into the hot water. That will clear the can a lot faster.

Final caution. Use gloves and goggles because refrigerant can be very nasty. Frostbite of fingers in seconds and blindness instantly if it hits the eyes.

Was the presumed need for oil lost in the process? Hopefully a full charge of oil wasn’t added.

EPA or not, this is why I don’t fool with AC systems anymore. Just gotta figure an AC problem is going to be about $1000 but that’s the price you pay.