The orifice tube is the restriction,

Neal

 

You mentioned 80lbs; that actually seems close to correct depending on the ambient temperature and humidity. What does not sound right is the drop in pressure to 30 psi. Low pressure should remain stable +/-5 to 10 psi on the low side. What is your high side reading during these times?

 

Ambient temperature is the key when checking pressures.

 

This is a good chart; however the official performance A/C chart for the Hummer H2 is even more extreme:


I have a cheap gauge that I got for free with a can of freon which has a low section, a green section that goes to 50 psi, and red "WARNING" section that is anything greater than 50 psi. For years, I use to freak out when I saw the low pressure go in to the 70 and 80 psi range, but now realizing, that's exactly where it should be.

Theoretically on an August day in Arizona you could see the low side at 106 psi which is still within the normal limits.

 

those are some pretty high discharge temps. on most vehicles there is a 30 to 40 degree temp drop out the center vents from ambient but those numbers seem quite low in the 20 degree difference cooling range. but it explains why my vents put out 60 degree air on a 75 to 85 degree day

 

These are 'Max' temps, not nominal. If your vents exceed this temp it means something is wrong with your AC. I have two trucks and tested both today with 96 degrees ambient temp at 54% humidity, one has over 150k miles on it and I got 61 degrees out of the center left, the other has very low miles and I got 51 degrees out of that same vent at the exact same temperature and humidity. However, both are well within spec. I had about 60 psi on the low port of the truck with 150k miles.

 

Another point to remember is that the blower fan speed can have an affect on duct outlet temps, the lower the fan speed the cooler the temperature.

 

Did the same job, new compressor etc, etc. For a 2005 (yours may be the same) it takes 1.6lbs of R-134a (not FREON) I used digital kitchen scales to weigh it in. On my 1st attempt I ran short of R-134a, may be 1.3lbs, the A/C was cool but not icy cool. When I topped it up to 1.6lbs it made a huge difference hitting -3.4C (26F)


this video worked for me:-

 

That's the proper way to check a/c temp, center vent in the shade!
I just checked my 3 sitting in the driveway under the hot sun @92°F ambient. Factory charge still drops around 50°F below ambient. Cold enough for me, since I drive with windows & sunroof open while the a/c is on.

 

Usually in the rain over here 🌧️