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2008 Pontiac G6 GT hardtop convertible (3.5L, 185K miles)
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Discussion Starter · #1 ·
I have a 2008 G6 (3.5L engine). We had the first heatwave of the year, so I turned on the A/C and... not much. The air was a little cool, but it wasn't ice cold like it was last year.

Today is much cooler, and I tried it on my trip to AutoZone. The air coming out was cool, but it wasn't cold. The low side pressure is:
  • With the engine off, having not used the air conditioner: about 140 PSI (the red "See Instructions" area of the can's built-in gauge).
  • With the engine on and the A/C running: about 32 PSI (green "FILLED" area).
  • Immediately after turning off the engine: about 65 PSI (just into the red area).
I took a peek into the engine bay, and the A/C clutch seems to be spinning normally, so I guess it's being commanded to run.

My low side, A/C-running pressure is in the green zone, but should I add more refrigerant to the system?
 

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I would check that your cooling fans are running as expected. Your AC needs airflow across the condenser to properly cool. If the fans are not running, airflow could be reduced (you get some airflow with forward motion). You could try a drive at highway speeds to see if the AC runs cooler as the condenser would be less reliant on the fan for airflow. Generally, a single AC gauge will not tell you much. From what I have read, you really need both the low and high side pressures to diagnose. Pressures can vary with temperature and humidity. Last time I looked at mine I think I had similar low side pressure - 35psi and a high at 200psi. Vent temps were 54f, so cool but not icy.
 

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Even if it's in the "green" zone on a gauge it may still not be quite enough. I recently had to charge mine up. I thought I had put enough in the first time as the vent temp felt pretty cool and the gauge was on the low side in the green. The next day it wasn't blowing much cool air at all. I tried again and put some more in and got it to around 35 PSI, maybe a bit more and it was blowing icy cold. It's been good for several days now. Also if the fill can is too low it may not be putting any more in. I had to swap to a new can the second time (I've got a stand-alone gauge that you screw the cans on) and I was able to get the pressure higher. Like boomer said, technically you're supposed to use gauges that read both the high and low side, but the single gauge that reads the low side pressure can still get the job done. My gauge also has a dial you turn to select the outside air temp which changes the min and max pressure zone.
 

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Even if it's in the "green" zone on a gauge it may still not be quite enough. I recently had to charge mine up. I thought I had put enough in the first time as the vent temp felt pretty cool and the gauge was on the low side in the green. The next day it wasn't blowing much cool air at all. I tried again and put some more in and got it to around 35 PSI, maybe a bit more and it was blowing icy cold. It's been good for several days now. Also if the fill can is too low it may not be putting any more in. I had to swap to a new can the second time (I've got a stand-alone gauge that you screw the cans on) and I was able to get the pressure higher. Like boomer said, technically you're supposed to use gauges that read both the high and low side, but the single gauge that reads the low side pressure can still get the job done. My gauge also has a dial you turn to select the outside air temp which changes the min and max pressure zone.
You can add more to get it up to the high side of the green and your AC air will get a bit colder. The other choice is to have it sucked down and refill it.
 

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2008 Pontiac G6 GT hardtop convertible (3.5L, 185K miles)
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Discussion Starter · #5 ·
Thanks, all. Even though it was "full" around 30 PSI, simply adding more refrigerant made it work. It was afraid to overcharge it, but it's now up to 40 PSI and pretty cold. Thanks for the help! If problems continue, I will get a proper double gauge and check the low and high sides.

(One last note: I heard this A/C system is both clutchless and can set check engine codes. I scanned for codes for the heck of it, to see if the computer wasn't starting it before the fill, and there were no codes set.)
 
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