mefferso

I assume there's an a/c compressor relay but can't seem to find one listed on the fuse diagram.

So, how do I jump the low pressure switch to get the compressor to run to pull the freon out my can to recharge?

alx

Is the system empty? If not What is the pressure? How did you arrive at the need for refrigerant?

mefferso

The system has no reason to be completely empty. I have no idea what the high and low pressure readings are.

I arrived at the need for freon based on typical symptoms of low refrigerant: a/c compressor clutch does not engage, intermittent cooling.

Also, its the easiest and cheapest solution. Makes sense to start with the cheapest first, right?

ItalianJoe1

So you're just gonna add freon to see what happens?

The compressor on those cars uses a refrigerant control valve to vary compressor displacement and thereby the amount of work it does. If that valve is failed (usually the problem), it will not cool most of the time, even though there's plenty of freon.

Why don't you have someone check the vehicle who actually understands how it works, before you just dump refrigerant in there.

FWIW, if the system is empty, the pressure difference from the full can to the empty system will allow enough to flow in to kick on the compressor if it's just waiting for the pressure to come up. It has to drop very low to disable toe compressor. However, if it's disabled and there are faults, it may not run until they are cleared. Needs proper diag to find the source of the not cooling issue.

mefferso

I just hate the idea of bringing it to someone and paying them to tell me the only issue is being low on freon.

mefferso

By refrigerant control valve do you mean expansion valve or is this an internal (non-replaceable) part of the compressor?

alx

Please hook up gauges to low and high side and troubleshoot accordingly. If you overload the compressor it will bog down and you will have a bigger problem. You might be low on refrigerant, you might have another issue.

mefferso

Dropping it off at a local shop tomorrow morning.

ItalianJoe1

The RCV is in the compressor. It is replaceable, but not sold separately by MB. I've replaced them for people, mainly on VW's, by buying the valves from a local a/c shop. Once the system is discharged there is a snap ring holding the valve in and it comes out, but you have to know which exact model compressor and valve, and a dealer or most shops will only sell the whole compressor.

mefferso

New a/c compressor and accumulator/drier on order to be delivered Friday. Shop wanted $450 for the labor to replace those. I passed on that and will just do the replacement myself. I had them completely empty the system and will have them recharge it correctly after i'm done with the install.

Can't find any DIY videos online. I found a couple threads here and the other forum that said it was fairly straightforward. I am open to any tips you guys might have.

Thanks

backdoc4you

mefferso...how did your job turn out? I suspect I need a new compressor on my 07 GL450. I'm pretty handy and am also considering doing it myself. Is your ac ice cold again? Thank you!

mefferso

Working great now! I did have to replace the compressor and drier.
It really isn't that bad at all. I started a new thread with the parts I bought and general how-to-replace steps since I couldn't find one anywhere online. https://mbworld.org/forums/gl-class-...ement-diy.html

backdoc4you

Mefferso....I received my compressor and dryer in the mail this week and am doing the job on Mother's Day. Just wondering if you also replaced the expansion valve? I am somewhat suspecting that it may have been at fault for malfunctioning and stressing out my compressor. Its only a $30 part but have zero idea as to how to replace it? Thank s for your opinion! Hope you AC is ice cold still....its 100 here in Phoenix

ItalianJoe1

Almost never the expansion valve, almost always just the valve in the compressor.

backdoc4you

ItalianJoe....I'm kinda hoping so. But I am downloading my new Mercedes WIS/ASRA virtual repair manual right as I write this. I already bought the expansion valve, and the repair shop I got a $2450 quote from of course wants to replace every AC part on the vehicle, so I might give it a whirl. Based on my symptoms prior to my compressor seizing, the expansion valve may have been malfunctioning. Repair quote gave a 1.8 hour labor estimate to replace it....we will see. I'll let y'all know after this weekend how it goes...
p.s. Go Juventus!

mefferso

What Italianjoe said. I didn't change it since it likely wasn't the problem in my case. At $30, maybe I should have. So sorry, can't be of much help as I did not look into how to replace it. Good idea with the manual download. Please do let us know how you do it.

Yeah, at 100, you definitely have to get that fixed soon. My wife's 7 months pregnant and 85 here (Louisiana) felt like 100 to her, haha.