GM charges the system with fluorescent dye at the factory. You can get glasses and UV lamp at the auto parts store.

You might consider Harbor Freight Tools, they have a manifold on sale for $50.
https://www.harborfreight.com/

 

There is a pressure switch on the AC system. If the refrigerant pressure is low, the switch prevents the system from turning on the compressor and fan. The compressor can be damaged if it is run for more than a minute without any refrigerant in the system. The switches have been known to go bad.

According to the Murray catalog this is the switch no 35970.


According to GM parts Direct, this is the location.


The switch is over $30 so I wouldn't just change it to try it. The best way is to check the system low side pressure with ac system gauges. The switch needs a pressure of 51 psi to close. It should be closer to 100 psi when the compressor isn't running. This might be the point to take it to a shop. You have to decide if you want to try to check further.

If I don't have gauges readily available, I disconnect the wiring harness from the switch. It should be a 2 wire connection. Then I use a wire to connect the 2 terminals in the harness. I do it with the engine running and AC on maximum cooling just to see if the compressor turns for ABOUT 15 SECONDS. If the compressor doesn't run, it is a different problem. If the compressor does run and the line that the switch is mounted in gets cooler, there is at least some refrigerant in the system. If it doesn't cool, there may not be any refrigerant left meaning a large leak. The condensers are vulnerable to damage from road debris as there is a hole under the bumper. If the system lost all of it's refrigerant it will need to be put under a vacuum to remove air and any moisture and see if the system holds a vacuum or has a large leak.

If the switch is bad a further test would be to use the jumper wire to run the compressor longer and see if the system cools well. If it does cool well I would try installing a new switch. There is a valve like a tire valve in the line under the switch so it can be unscrewed without losing any freon.

There may not be enough refrigerant to close the switch. Refrigerant can leak slowly from the compressor shaft seals especially in a 10 year old vehicle. As long as there is some pressure, like about 20 psi left, the system is still fairly well sealed and no air or moisture has entered. Refrigerant can be added using one of the kits on the market.

 

Update to the thread:

I finally got around to the AC. Summer is pretty much over, but I want to be prepared for next one.

When I got my oil changed, I asked the guy at the shop to check the pressure on the AC, and there was none.

So I had her filled up, and within 1/2 day it was gone... so, big leak apparently.

I bought a can of a-134 with UV dye (no sealant, I don't want to gunk things up) and a UV flashlight.

The result?

Not good news. I can't find any dye anywhere... except a few dots inside the AC vent...

So I'm thinking it's probably the evaporator core or the expansion valve... but either way, a horrible dash job.

So... I was wondering, since I'm probably going to either go in there myself, or pay a mechanic to do it... what else would you guys change?

I think I'll have the heater coil changed out while it is all opened... whether it is my time or someone else's, there are hundreds of dollars of work going into getting there... might as well change out all that could fail in a vehicle that has 13x,xxx miles on it.

 

Oh, I also changed out the thermostat... which got the fan going. The AC compressor clutch started engaging after the AC reached the right pressure. The AC works perfectly while it has pressure and refrigerant. Oh, just a refresher, the car is a 2006 and is a FL native... so AC has been running in high temperature and high humidity pretty much the entire life of the car.

 

Problems in the dash can be a huge pain to get to. It makes me want to find the people who designed the systems and subject them to a long painful torture as well as neutering them and their progeny because stupid people shouldn't breed. Proper design could allow for a quick and easy component change but these engineers don't ever consider that things in the dash might need to be replaced at some point. If I was in management of an automaker I would require things to be designed so components could be replaced in under an hour.

Usually there are YouTube videos available for many of these repairs but I don't see any for an evaporator replacement or even dash removal other than to change the radio. It can be difficult to figure out how the dash is held in place. It is installed in minutes in the factory but removal can be more difficult. They use push in connectors that sometimes don't come out without breaking the plastic pieces, especially on a ten year old vehicle. It helps to know here they are and what angle they are at which is where the videos come in handy.

If it leaks down over two days, the hole has to be rather small. A hole as small as 5 thousandths of an inch could leak that over 2 days. As bad as your leak is, sealer might not help but I would try it first IF IT WAS MY VEHICLE. I have had success with AC Pro Super Seal including 2 evaporator leaks. I would vacuum the system down to see how long it holds vacuum then install the sealer and freon.