So I went to recharge my A/C today, if nothing else to see if there's a leak somewhere.

I ran a vacuum on it for a good hour, and let it sit for a few days to ensure there were no leaks. Lo side sat at 29.5inHg for a week without budging, so I figured I was good to go. Got myself a couple cans of R-134, some UV dye to look for leaks afterwards, HPtuners so I could set idle to 2k rpms and off I went.

It took a bit of futzing with the can to get it to open properly, but once I did I saw the pressure on the gauge jump to around 25-30psi. I followed the can instructions (tilting it 90 degrees every few seconds) but wasn't really seeing the can empty itself (nor see any refrigerant flowing through the sight glass). I kept futzing around, trying a handful of things to see if I could get some change in the system but nada. All I could ever see was a slight dip in pressure if I closed the valve on the can. Eventually though, the pressure on the lo side jumped (i assumed this was because of the rising underhood temps, even tho I had a couple of fans running) to around 70 psi. Still no change in weight on the can.

Right now, I'm seeing around 75psi on the lo side, and 130 on the hi. I'm assuming this means my compressor is likely shot?

 

Low side high and high side low is usually a compressor malfunction.

 

It does not sound like you got your 2 cans of r134a in the system. With an evacuated system, you should pull in enough charge to see the high and low side pressures somewhat close to ambient temperature; 80 degree ambient is about 80 psi. Once the previously evacuated system takes in all it can, starting the car and turning on the a/c will empty the first can. Did you see anything like I am describing?

 

Not at all. The system took in maybe half of a can. According to the service manual, i shouldnt really see much higher than 40psi on the low side. That, plus I'm not seeing anything on the high side close to the normal readings.

 

OK ... Let's start with the basics. You evacuated the system, and it held vacuum. GOOD.

Now - were you using the small cans of R134 available through places like Wal Mart - or were you using the 30 Lb "Tank" of R134 ? My guess is that you were using the small (less than 1 Lb) cans. Those cans come in two flavors - self sealing and not self sealing - the "tap" you use to pierce the can has to match the kind of can you have. If you try to use a tap for a non self sealing can on a self sealing can - it won't go well . (Most newer R134 cans that you will find in stores today are the self sealing type - most of the older can taps are for the older - Non-Self Sealing Cans)

Now - as for the actual charging process - in theory - the refrigerant gas will be at a pressure that is governed by the ambient temp. As you charge the system - you will get some refrigerant into the system based on the pressure difference between the can and the system - then the compressor will have to run to drop the intake (low pressure) side below the pressure in the can.

Based on the numbers in your post - the compressor was running - otherwise low side and high side pressures would be basically equal. Yes - there is a very decent chance that your compressor is N/G - BUT - the C5 A/C takes about 1.75 Lbs of refrigerant - you did not get nearly that amount in. So ... I would say that you need to try add more refrigerant before condemning the compressor (or any other component).

First off - make sure your can tap is appropriate for the kind of R134 Cans you have.

Second - While there are some that will not agree with this - I would suggest holding the can of R134 upside down as you try to charge the system. This is frowned upon because doing this means that you're inserting liquid refrigerant into the charge line. The compressor is NOT going to be happy if it tries to compress liquid refrigerant - so you need to regulate the flow (by using the valve on the charging manifold) so the flow is very slow, and the liquid refrigerant has time to change phase (to a gas) as it flows into the system. I've done this a number of times on both car and home systems, and it's not hard to do... You want it to take a few minutes to empty a small (sub 1 Lb can) of refrigerant.

I've attached an R134 Charge table below.

 

D'oh. I did not realize that there were different kinds of R134 cans. All of my experience doing A/C work was with those fancy machines that just do it all for you lol. I looked and the cans are definitely the self-sealing, and I'm going to assume my tap is not the correct kind (which would explain the issues I was having while attempting this). Fortunately it looks like Harbor Freight has the correct tap, I'll pick one up tomorrow morning. Thanks for the information! I'm going to keep my fingers crossed that the compressor is still good.

 

I am going to guess that you may have pulled air into the system if you were using the old piercing style charge hose on the new resealing style and should evacuate again. As I wrote earlier, you should get enough r134a into the evacuated system to get it to run and then empty that first can. Then you can use the running system to pull in the second can. Assuming they are the 12 ounce cans, you will still be a few ounces short of a full charge.

 

If you use a small bucket of hot water you can raise the pressure of the r134 cans sufficiently to overcome system pressure. Two 12oz cans are just shy of a full system, and enough to run cold. Be sure to keep the cans upright.
Holding vacuum is a good overall indication of system integrity — but it misses one important and common leak path: the Schrader valve the gage is connected to. Since you have a gage set, check your vacuum from the low side port with the high side disconnected and the high side with the low side disconnected.