2008 GL320 AC issues
 

Wife said AC took a while to get cold. This past weekend I checked it out and it was cooler on right side than left. This appears to be like a 210 does when it is low on refrigerant. I recovered the system and it was about 1/2 lb low. Recharged it and it was cooling great. I was out of town and she has been driving it all week and it was fine. Got home today and we went to town and it is suddenly not cooling at all. Worked fine yesterday she said. I will say before I did the recharge I noticed it would blow hot, then all the sudden start cooling again. I just figured it might be doing it because it was a little low. Also the last time I was in it before I did the recharge I noticed it would cool, then start blowing hot and suddenly start blowing cold again.

I just hooked it up to SDS and it shows its calling for compressor, nothing locking it out like low pressure. No error codes. Pressure shows 10 bar with or without it calling for compressor. With this compressor it turns all the time so you can't tell if its engaged or not. I guess tomorrow I will have to run thru the tests which appears to be testing resistance at one of the plugs on the back of the acc panel, then go from there. Is there a common failure on these it could be? Looking up parts it appears expansion valve might be electronic? Maybe compressor died?

Sounds like it may be new compressor time.

Yep its the compressor. BTDT on my son’s 2008 ML320 (and other son’s 2008 E320, same issue).

These are variable displacement compressors, the command wire is not a solid +12 V but a PWM signal. This is used to modulate a valve inside, that uses the pressurized refrigerant to change the swash plate angle of attack. This causes the pistons to pump more or less as needed to fulfill the demand.

When this mechanism fails, it usually results in the swash plate staying at minimum angle, so you get no cooling (this is what it is commanded to do when you need no A/C). If you grab the hub at rest and it spins freely, the compressor isn’t seized, so therefore it did not self destruct, and you’ll only need to change the compressor and the receiver dryer (long tube under the condenser behind the front bumper).

If the compressor seized however you’re looking at replacing the condenser, evaporator, exp valve, and flushing the lines.

WIS instructions are pretty straightforward for replacement, it’s on the bottom left side, fairly easy access. Go ahead and pull the bumper and left side wheel well liner it will make it much easier to access, you need to pull the bumper to get at the dryer anyway.

I ran across a service bulletin for my 05 cdi stating the low pressure hose from the compressor to expansion valve collapses internally. It also listed many other affected models but I can't seem to find it presently.

In the SDS tool check the running amps of the refrigeration compressor valve, if its stuck at 0.99 amps and you are stuck with 10 bar liquid line pressure, the valve is not working. You can replace that valve (its available aftermarket) - you will need to physically check the valve and then buy a replacement, its only held with a circlip but you will need to completely remove all the refrigerant before you do this.

You will also need to remove the compressor which isnt too bad either. disassemble the hoses from the top part and leave them on the compressor and use the hoses as handles.

Make sure that you buy a valve with a diode built into it, otherwise you will have a permanent error code and no AC at all, if you do happen to not find a diode valve and only can buy a plain valve then you can add a schottkey diode to the wiring pigtail on the compressor itself to make it work, Ive done it on quite a lot of cars/suvs recently due to the supply chain stupidity going on. (cant buy decent parts)

once everything is installed, vacuumed, filled and running you will see the valve amps being regulated between 0.3-0.5 amps with a cold cabin and also on sudden acceleration of the engine and an almost fixed vapour line pressure reading but changing liquid pressure reading depending on outside temperature.

p.s. you can also buy a pulley kit for these compressors if your pulley and hub are noisy, if the compressor is making a whiny noise while running, its bad and requires replacement.