Hey everyone I got my E320 in 2020 with 250K miles on it and a pretty whooped body. I have been using this forum since then for tips on maintenance etc. since then and have managed to get it in pretty fair shape. Thanks for all the great info you've compiled here.
I have run into an issue that has me a bit stumped so here I am asking for your help! I have read through just about every thread I could find relating to the AC system and the various faults that occur.
My AC gradually stopped blowing cold the summer before last (over about 2-4 weeks) and now just blows basically ambient temperature.
I actually took it to a local shop for diagnostics because I suspected a leak and didn't own the equipment to test it myself. They told me they discharged my system and were not able to get it to recharge (delivered it with 7bar on sensor #7 readout, it was returned to me with 2bar).
The shop proceeded to try and sell me on $1800 in repairs without being able to actually explain to me what they thought was the issue (sounded like they just wanted to throw parts at it and replace most of the system), so I walked with my pocket $200 lighter and no more info than I started with.
I went out and took the readings this morning and got:
1: 94
2: 67
3: 73
4: 75
5: 71-73 ( was bouncing)
6: 82
7: 02
8: 67
9: 27
10: 1.3
11: 2.3
12: E
20: 3.2
21: 46
22: 00
23: 32
24: 13.5
40: 164
41: 91

I also had error code b1234 which I understand is unrelated to the ac system.

My ac clutch appears to be functioning normally, it turns on and off in the expected manner. I tried to add some 134a to the low side today and it accepted a small amount but wouldn't go past 4bar.
I went and rented an AC pressure gauge set and have included a photo if the readings I got for the high and low side. I have also included a picture of my car

Based on the fact that the compressor is running but it wont accept a charge does that point to a faulty control valve inside the compressor?
Any info and help is greatly appreciated!

Thanks,
-Miles





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My experience in AC system is somewhat limited, but from what I understand, IF, the shop really discharged the entire system, they/you need to evacuate the system. Without it, you won't be able to put any refrigerant in the system. So you need to find out if they really discharge the system. At the same time, you can ask them if indeed they did discharge the system, why they didn't evacuate the system.

You have a leak somewhere in your system. with the gauge hooked up, evacuate the system and see if the system hold. See if the system holds for at least 30 minutes. If the gauge reads 0, then evacuate the system again and shoot some UV dye in it. Your refrigerant will leak out, but this is the only way to find where the leak is/are from, unless you take it to professional (You know you not supposed to take it back to the first shop you mentioned). While at it, pick up a cheap black light from evilbay or wherever you prefer. When the AC started to get warm, get your black light and start hunting for the leak. Most of the time, and I said again, most, will be from hose connection like deteriorated O-ring(s). If and when you find the leak, please take it back to AC shop and have them discharge the system before you make any repair. Even you don't have any cold air coming out from the vent, the system is still pressurized to a certain point. It's good for both the planet and you.

Lastly, your gauge picture shows the pressure is way too low on both side.

BTW, normally, the system have some kind of cut-off switch to turn off the compressor when the system pressure is too low. Don't our car comes with it? If so, compressor shouldn't be running with pressure that low. Maybe you're at just above the cut off point. Maybe someone with more knowledge can jump in and confirm this. I'm a MB newbie as well. I'm still learning about our E320 as we go.

 

Sorry, to be clear, the system was properly evacuated by the shop and had vacuum pulled on it for 2 or so hours. The shop told me they didn’t detect a leak. When they went to refill the 134a they said they could not fill it with more than a little bit (2bar).

As far as the pressure gauges go, I thought the low side pressure was supposed to be about 2 bar (30psi or so) and the high side double ambient temperature plus 50psi as a rough measure (so about 180psi for 67F ambient temperature).

The fact that both the low and high side have about the same pressure reading makes me think that although my compressor clutch is engaging there’s some sort of internal leak in the compressor that’s not allowing it to build pressure.

As far as the compressor engaging at that low pressure there is an override you can enter from the hvac controls. It appears the shop changed mine, although the value isn’t correct (usually the number is set at 136 and you add 16 to force the compressor to run.

 

Sorry, for some reason I was looking at the red readout instead of the PSI/black marks. The outside BAR readout should have gave me a hint, but maybe I was tired.

But I think you're on the right track. Low side shouldn't be that high, and high side shouldn't be that low. From my past experience, it's usually a bad compressor. Had few different this and that but can't remember what was it. Besides, it was from different cars and wasn't mine. You tend to forget what was it if it's not your car.

I guess you need to discharge the system and change out the compressor. Evacuate the system again and recharge it with correct amount of refrigerant. Don't forget to add the oil when installing the new compressor.

Don't feel so bad. At 250k, it lasted. I have/had different cars that needed to replace the compressor almost at every 5years/35k miles. Been in middle of nowhere, we need to run the compressor whenever we drive all year round. We don't have winter here (we do but you mainland people will laugh at us when we say we're cold) so we drive the compressor to it's death. And need to replace it ASAP.

 

Nice wheels