Have a 2000 express with ac issue that popped up yesterday. Thought compressor was gone, but it kicked in again later. Kicks in & out. Comp doesnt sound good when it kicks in, but then it's quiet. Low side connection is different fitting than the 134a on other vehicles. Was able to connect to the port on the acccumulator & got 35 psi at 75 ambient.

I'm thinking a pressure switch is tripping it out. What am I looking for in a good high side pressure?

Do I need an adaptor to connect to the port to test my suction pressure for the 410a guages?

I'm certified as a universal AC tech, including MACs but have never really messed with the automotive side of it.

Any input is appreciated.

There should be a low and high side fille/test port R-134a quick couplers in behind the right side battery or at the side of it area.

With compressor running or jumped and running you should see 25-35 lbs on low side.
Always check at idle and then at 2K rpm.
Cut off is around under 26 lbs on low side switch and high side cut off may be close to 400 or more.

After the the 12 volt ac request makes it threw the low and then high side switches it goes to the computer and then from computer to a ac clutch relay.

If you need a wiring diagram I can try to post it to you.

Good High side will range from 250 to 350.

Thanks for the info. Learned alot about the system in the past week. Found that the clutch was ng. Bought and tried to install a new clutch....a disaster. Had the puller tool and still broke off the end of the shaft.
Got a compressor from a truck that we have for parts, a identical match, but it siezed before I got the first lb of 134 in.

Bought a new compressor from autozone for 269.00 and installed it per the directions including draining, measuring and adding new PAG oil. Fired it up, charged it and I have A/C again. Yay.

One thing was weird though. My truck has a label that calls for 3.0 lbs of charge, but showed low pressure after I weighed it in. Had to put in almost 4.5 lbs before I got the pressures It was calling for. The Haynes manual lists it at 39/251 psig at 80 degrees ambient. I settled for 35/200 after 4.5 lbs & it seems to run great.

What I learned today:

:nono: Replacing the clutch is a complete waste of time unless you have the tools and experience to do it. The clutch was 140.00 and the whole compressor with clutch is 269.00. The tool to remove the clutch is another 29.00. The ease of putting in a new compressor...priceless.

:popcorn: Automotive A/C is so much more interesting that residential. The systems are pretty complicated. My compressor is the size of my alternator and it's 6 cylinders! You know I'll be taking the old one apart.

You are welcome.
And thanks for posting back how it went.
Strange on it taking 4.5 lbs of R-134a.

35/200 is good pressure.
I always like to speed up to 2K and check pressure there to.
26-30 and 250-300 at 2 K is good pressure.

The lower you can keep low side to around 28-30 is better cooling you get.

28-30 low side should give you around 40 degrees vent output.
The old rule on auto AC is 1 degree tempt for one lb of pressure.
Good luck
MT