Over the past few months, I noticed my Air Compressor starting to be difficult, sometimes it would engage right off the bat from me hitting the AC Button, other times I would have to mess with it a bit, turn temp all the way up then all the way down, or sometimes even start driving before AC would kick in. Now my AC is fully not kicking in, no matter what. At the time, I figured it was the compressor on its way out, but now im realizing that the clutch isn't engaging while the car is running and I hit A/C button, simply nothing happens. I figured the clutch might've went, so I ran the IPDM test where it tests the AC clutch 5x, and the clutch seems to work just fine. The IPDM is intentionally not sending the signal for the clutch to engage while the car is running, leading me to believe the system has low pressure. I checked the pressure using an auto zone tool rental gauge with both a hookup for the high and low pressure sides, but the compressor won't actually kick on, so Im not sure if I was able to get a proper reading. The reading was 0. The question is, how do I go about getting a reading, or even topping off the R134a if the compressor won't even kick on to allow me to do those things?

Use a wire and jump 12v power from your battery to the compressor clutch solenoid. That will keep it engaged and running so you can test the pressures.

Unplug the low pressure switch and stick a paperclip in it to jumper it, then the AC computer will think it's got pressure. Doesn't need 12v, a paperclip will suffice it's just a 2 wire system, the low pressure switch just turns on/off depending on pressure behind it.

The low pressure switch might also be bad though, it screws into a metal fitting, behind the sensor is a schrader valve like for airing up your tires, this is so you can unscrew and replace that low pressure switch without actually discharging the system.

If you jumper the low pressure switch and get good readings for pressure with the system running take a digital multimeter and check for continuity on the switch itself, it SHOULD be closed / have continuity. If it does NOT have continuity (open circuit) but the pressure reading is good (like 30-50psi depending on ambient temp) then it's probably a bad low pressure switch.

If you do replace it, when unscrewing it you MUST COMMIT to unscrewing it, it's going to leak out a little refrigerant while you're unscrewing it, not much just a tiny bit but if you stop and let it keep leaking you will eventually run out, just commit and keep unscrewing until it pops out then it will stop leaking.

Is the same true for the high pressure switch? I broke what I assume must be the high pressure switch off of the compressor while doing other work. My AC still works so I've just been letting it ride. But if it were possible to remove that switch without evacuating the system, I'd replace it. I assumed if I unscrewed that thing it would let all the refrigerant out all over me.

My wifes car needed front bumper cover replaced, I ordered one , had it painted instead of doing it myself (because its pearl white and wanted it to accurately match color!). While i was at work HER nephew and his ratger arrogant buddy offered to put the bumper cover on (for a small fee, in their opinion, in my opinion they just saw a way to make a quick coin) Well dumb and dumber started working on the deed, first step was to REMOVE THE PROTECTION PLASTIC static wrapping the bumper cover!!!!! OMG why?! Its there to protect it, remove it AFTER its installed idiots!!!! well she called me about the time they started turning wrenches on the front of her car, she called to ask if i wanted to keep the plastic bumper wrap for another project, i told her MAKE THEM STOP NOW! But not after my WIFE's nephew (that thinks he is mechanically inclined) some how decided that the second step was to REMOVE THE Radiator and Condenser and thankfully but also crapp-ully tHe first thing thing he did was to remove the low pressure switch (not unplug it no, REMOVE IT!) And he got startled when it began to leak Freon and so stepped back and just let it go! Well my wife was more mechanically able than he was and so she went out there (hearing the leaking through the screen door) and demanded he screw it back in saving some of the freon and also preventing the system from just sitting with an open hole in it for bugs, dirt, dust, pollen, Bill Clinton, and condensation to make a home inside her A/C!!!!!

Well she fired dumb and dumber but then u couldn't get the car to take the refill of freon!
Insert this post here and i did the paperclip trick and now her bumper cover is installed AND her A/C has never blown colder! So here is the kicker, just because she LOVES her family she likes to say her nephew is the reason she has colder A/C! Not me, not you for creating the post responsible for teaching me to get the job done NO!!!! Dumb and Dumber are the sole responsible party for her A/C blowing so cold.
So we must make the time to thank them for a job , well, not done right and not even done at all !!!!!!

Anyway, if you read my "sucky" tale then you know now
"There is NO such thing as gravity! The world just SUCKS!!!!" 🤣

☆☆☆Thank you for taking the time to reply and imparting the knowledge!!!!!!