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Discussion Starter #1 (Edited)
Anybody know what the correct a/c refrigerant pressure is supposed to be in these cars?

Let me give a little background in the hopes that someone may spot something I have missed.

To begin with, the a/c system had sprung a leak about 4 or 5 months ago in a rubber hose by the receiver-dryer, so I had any lines and seals that were rubber replaced, and I also had a new receiver-dryer put in and changed the expansion valve for good measure. After doing this, the system would absolutely freeze your butt off even on a 90+ degree day with the pano top on.

Separately, the automatic a/c has been acting up for the past year or so. It would randomly turn the heat on when I was driving the car on a 90 degree day, or would just act weird. I could always override it by just turning the temp all the way down to "LO" and then controlling cabin temp with the fan speed, so this was only a minor annoyance.

But eventually, it got to where it would screw up all the time and so I took it into the dealer and told them I suspected the cabin temp sensor. They tested every sensor in the system (refrigerant temp sensor, evaporator temp sensor, etc. etc...something like 5 of them in total) only to confirm what I originally thought, which is that it was a defective interior cabin temp sensor. The fact that you could always override it by going to "LO" kind of gave it away, but they insisted on doing the diagnostics anyway...go figure. So I told them to replace it, and they did.

Then I picked the car up from getting this done, and now the automatic a/c works fine again, but the damn refrigerant system isn't working right now. I feel like I am on a treadmill with dealers lately, with them fixing one thing and breaking two more, but that's another story. Anyway, whether you have it on automatic or set on LO, or anywhere in between, it just doesn't get as cold as it did before, or even cold enough to make it comfortable inside the car. I also hear whistling in the refrigerant lines running to the evaporator when I step on the gas or the engine changes speeds.

So I took it back to them again and told them I thought it was low on freon, and they went and hooked it up to the machine and then came back and told me that it was full. So I asked what the reading was, and they said 2.08lbs. I then said "well, maybe you guys knocked something loose when you were pulling the refrigerant temp sensor out and it got lodged in the expansion valve or something", and they said that wasn't the case, and that the high/low differential was where it should be. They also said "well it blew 48 degrees at the vents", but since they have a fully-airconditioned workshop that's already 70 inside, I bet that probably has a lot to do with the vent-temp. It sure doesn't blow 48 when you drive it outside, lol.

In any event, they gave me a "NO FAULT" report and sent me on my way, but now I am freakin' dying in this car. I don't even want to drive it anymore, because I just sit and sweat. It doesn't drop below 78 degrees in the cabin on a hot day, and it just isn't what it used to be before they screwed with it 2 weeks ago.

So, any ideas? They swear it's not low on freon at 2.08lbs, and also say there's no blockage based on the pressure differentials. So what's the actual charge level supposed to be? Anything else you guys see that I am missing?

FWIW, I got the electric fans working again awhile ago, and the car sounds like a hoover vacuum now...so it's not those. My engine fan clutch was also replaced awhile back, and it blows very strong. So I don't think it's the fans...especially because that was all corrected way before the a/c issues cropped up.
 

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it depends on outside air temp on the hi-pressure side.

mine says 2.1 lbs on the placard.
 

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Discussion Starter #3
it depends on outside air temp on the hi-pressure side.

mine says 2.1 lbs on the placard.
Well they said mine was 2.08, so it looks like the dealer was right. I don't see how 2/10ths of a pound would make any difference whatsoever, let alone the difference I am seeing.

Anybody got any other ideas?
 

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Did you pull the DTC codes from the A/C Pushbutton Control Unit in the dash? What readings/codes did you get?

When you wrote...Separately, the automatic a/c has been acting up for the past year or so. It would randomly turn the heat on when I was driving the car on a 90 degree day, or would just act weird. I could always override it by just turning the temp all the way down to "LO" and then controlling cabin temp with the fan speed, so this was only a minor annoyance.

makes me think that it's possibly the monovalve or one of the many sensors intermittently failing. The diagnostics should help pinpoint.

Bob
 

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I Had A/C Problems In The Florida Summer TOO!

A while ago, (Before I basicly replaces the entire A/C system) I had a similer problem. The air was cold but then I developed a leak in my condensor so I replaced it and the expansion valve and the dryer and had the system evacted and chrged and then proceded to sweat every time I drove anywhere. I had the same problem with my cabin sensor but it didn't matter at that point because it was always on MAX just to get to a sweltering 79 -81 depending on the time of day, it was cool at the vents but that dosn't matter, as you know. So I took it back to the shop and got the same thing you did....all ok. I read everything I could but nothing made any since to me. Then I was up in Lakeland Fl visiting a friend and we were driving somewhere and he asked what was wrong with my AC, I told him NOTHING! LOL. He suggested we take it over to this guy who runs an a/c shop....at his house! I was like....umm I don't think so, but I ended up there, actually a pretty nice shop. He pulled it in and checked a bunch of stuff and came back to me and said that my compresser, though working was only pumping at half the capasity and that it was dead (I don't remember what his copressor readings were....maybe 28psi or something) anyhow they were supposed to be double what I was getting. He said this was commom with Mercedes Compressors, they would start to die, but not like other makes that just implode on themselfs and quite working. My low and high side pressure readings were normal, but he did something to test the compressor itself. Well I replaced it and the A/C blowes cold as it ever has......

Hope this helps you,

In the meantime keep a samll sweat rag in the car!!!!

Brian
 

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Discussion Starter #6
Did you pull the DTC codes from the A/C Pushbutton Control Unit in the dash? What readings/codes did you get?

When you wrote...Separately, the automatic a/c has been acting up for the past year or so. It would randomly turn the heat on when I was driving the car on a 90 degree day, or would just act weird. I could always override it by just turning the temp all the way down to "LO" and then controlling cabin temp with the fan speed, so this was only a minor annoyance.

makes me think that it's possibly the monovalve or one of the many sensors intermittently failing. The diagnostics should help pinpoint.

Bob

What's the procedure for doing that? I will definitely try that out!
 

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Discussion Starter #7
A while ago, (Before I basicly replaces the entire A/C system) I had a similer problem. The air was cold but then I developed a leak in my condensor so I replaced it and the expansion valve and the dryer and had the system evacted and chrged and then proceded to sweat every time I drove anywhere. I had the same problem with my cabin sensor but it didn't matter at that point because it was always on MAX just to get to a sweltering 79 -81 depending on the time of day, it was cool at the vents but that dosn't matter, as you know. So I took it back to the shop and got the same thing you did....all ok. I read everything I could but nothing made any since to me. Then I was up in Lakeland Fl visiting a friend and we were driving somewhere and he asked what was wrong with my AC, I told him NOTHING! LOL. He suggested we take it over to this guy who runs an a/c shop....at his house! I was like....umm I don't think so, but I ended up there, actually a pretty nice shop. He pulled it in and checked a bunch of stuff and came back to me and said that my compresser, though working was only pumping at half the capasity and that it was dead (I don't remember what his copressor readings were....maybe 28psi or something) anyhow they were supposed to be double what I was getting. He said this was commom with Mercedes Compressors, they would start to die, but not like other makes that just implode on themselfs and quite working. My low and high side pressure readings were normal, but he did something to test the compressor itself. Well I replaced it and the A/C blowes cold as it ever has......

Hope this helps you,

In the meantime keep a samll sweat rag in the car!!!!

Brian
That's exactly...and I mean exactly...what's happening.

And the dealer thinks I'm nuts and is sick of hearing me complain about it, because they hook it up to their equipment and everything reads out fine. Plus, I think they get confused because their entire shop is air-conditioned...so they would tend to think that even the most anemic system is working fine, because it's already cold in the shop when they're testing it. It really doesn't take a good a/c unit to make a 20-degree differential when the ambient is already 70, and the minute I drive off the lot I start sweating.

I think I will find a shop that only does air conditioning and take it there this week with instructions to check the compressor. But ugh...compressors are expensive. I guess we can add this to the $6k or so I've already spent on maintenance in the last 6 or 8 months...and almost $3k of it has been on the a/c system. That has been a huge trouble-spot for me lately. Both this year and last, as summer approached and it started getting up into the mid-90s, I have had multiple a/c issues. How come it can't crap out in the middle of winter? Lol...
 

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Discussion Starter #8
Oh, wonderful...parts.com is showing $887.50 for the compressor. Grrrrreat....
 

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Chris, before you change the comp. find an Indy that will just put a set of gauge's on it and read the pressure's. The low side press. is what your interested in. Depending on the ambiant temp. the pressure should be in the NEIGHBORHOOD of 38-50psi. The 2.08 that they gave you is the capacity of the system NOT the pressure. 2.08 Lbs of R134A is how much GAS should be added to a COMPLETELY empty and vacumed A/C system. If the A/C system is full of gas, you should have 38-50 psig low side and I'm GUESSING 150-200 psig high side. If these #'s are close, then you have a "Control System" problem!! If these #'s are way off, then you have a sealed system problem. Hope this helps.
 

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Discussion Starter #11
Chris, before you change the comp. find an Indy that will just put a set of gauge's on it and read the pressure's. The low side press. is what your interested in. Depending on the ambiant temp. the pressure should be in the NEIGHBORHOOD of 38-50psi. The 2.08 that they gave you is the capacity of the system NOT the pressure. 2.08 Lbs of R134A is how much GAS should be added to a COMPLETELY empty and vacumed A/C system. If the A/C system is full of gas, you should have 38-50 psig low side and I'm GUESSING 150-200 psig high side. If these #'s are close, then you have a "Control System" problem!! If these #'s are way off, then you have a sealed system problem. Hope this helps.
Awesome, thank you for those figures, they are about to come in very handy. I am planning on taking it this week to a shop that only specializes in AC repair, and I will ask them for the high-side and low-side readings and will report back to you when I get them.

I think I will also ask them to record the readings at idle and the readings at, say, 4000rpm. That will narrow it down, if it is a compressor-clutch problem. In fairness, it does work better at higher rpm's so that might be the case. Same end result, though...I don't think anybody sells a clutch without a compressor so I'd still have to replace the whole thing.

I have got to do something, for sure. It is now officially summer in Florida and it's between 95-105 degrees every day. The car is pretty much undriveable as it sits, unless you are going somewhere where you don't mind showing up completely soaked in sweat-stains.
 

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Chris, The one thing I didn't mention is these #'s are at ABOUT 75degrees ambiant temp. The HOTTER it is, the higher the pressure will be. Not a lot higher,but higher. From your description, It ALMOST sounds like you have a leak somewhere, and the evaporator is ICING up from lack of a FULL charge. Let us know what the Indy finds.
 

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Man o man here i go. Nice thread Kinda tugs at your heart strings.

I to am starting to go down the REPLACE everything that has to do with the AC system. Last year My coolant ran out and i let it go over the winter cause the Stealer said i had a leak in my compressor and not to worry and get it fixed next summer. So today i took it to my indy, NOT THE STEALER, and get a charge and the leak is actually in the Hose from the dryer. 560 just for the hose. the dryer is not so bad as for cost. Next week its all gonna go down. Thanks for this post cause it helps that others have felt the pain!
 

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Discussion Starter #14
Man o man here i go. Nice thread Kinda tugs at your heart strings.

I to am starting to go down the REPLACE everything that has to do with the AC system. Last year My coolant ran out and i let it go over the winter cause the Stealer said i had a leak in my compressor and not to worry and get it fixed next summer. So today i took it to my indy, NOT THE STEALER, and get a charge and the leak is actually in the Hose from the dryer. 560 just for the hose. the dryer is not so bad as for cost. Next week its all gonna go down. Thanks for this post cause it helps that others have felt the pain!
I wish mine were just a hose. My compressor really does appear to be the problem. I have deferred dealing with it for the time being because I have a lot going on, but I will replace it before summer's out.

The indy did the same thing the dealer did, and just hooked it up to the pressure guages and told me everything's fine. Except it's not, and it doesn't work right. These people get so short-sighted, you know? I don't care what the guage says, I only care that it won't freakin' cool the car.

But the compressor's the only thing it could be at this point, since I already replaced the expansion valve and the receiver drier, I already had all the sensors gone through and ruled out icing, and there aren't any leaks or anything anywhere else (dye test). I also had it evacuated and recharged twice, and was there watching it personally, to make sure the oil charge was done right, so it's not that either. It just has to be the compressor.
 

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compressor is easy in my eyes. Seems like u did all the hard stuff. I am waiting for "OK so the hose and dryer is replaced Now there is a leak in the compressor." I do trust my indy guy. I had my evaporator changed out when i bought the car not on my dime either, dealership. ANOTHER GREAT STORY :) :) :) VERY VERY happy about that. So i THINK i can sleep well that that will not need any work.
 

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Discussion Starter #16
compressor is easy in my eyes. Seems like u did all the hard stuff. I am waiting for "OK so the hose and dryer is replaced Now there is a leak in the compressor." I do trust my indy guy. I had my evaporator changed out when i bought the car not on my dime either, dealership. ANOTHER GREAT STORY :) :) :) VERY VERY happy about that. So i THINK i can sleep well that that will not need any work.
Those evaporators are notorious for springing leaks, so it's good you got that out of the way already. I think you will be all set now, but still...shame on that dealer for trying to take you for $1k on a new compressor when it was just a rubber hose. I swear, doing business with some of those guys is like walking through a snake pit.
 

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Before you guys go spend your $$ on compressors etc.
Have short the temp. sensor on the drier color RED it controls the aux. fans.
If you are happy, then replace it with a GREEN color one.
And think about all the money I have saved you.
Regards.
aam.
 

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funny u should mention the Aux fans cause they are not working correctly either. That is next on the list after the ac pieces. gonna start with the aux fan fuses though. ;)
 

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I had AC problems in my 94 SL500 as well. What I ended up doing was to get the Nippon part number off my compressor and see if any other cars where using the same setup. Well, it turns out that a 1994 Grand Cherokee and a 1995 Vette ZR-1 uses the same compressor. I then went on E-Bay, bought a rebuildt compressor for $39,-. I had to use the main shaft from my original compressor, but otherwise they where identical. Mounted it, filled the system and it has worked for three years without a glitch. Being in Las Vegas we see 110 on a daily basis and the car is coool.. The one thing I never got to was the light bulb for the temp indicator. I took the controller out but could not see any bulbs to be replaced.
 

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Discussion Starter #20
I had AC problems in my 94 SL500 as well. What I ended up doing was to get the Nippon part number off my compressor and see if any other cars where using the same setup. Well, it turns out that a 1994 Grand Cherokee and a 1995 Vette ZR-1 uses the same compressor. I then went on E-Bay, bought a rebuildt compressor for $39,-. I had to use the main shaft from my original compressor, but otherwise they where identical. Mounted it, filled the system and it has worked for three years without a glitch. Being in Las Vegas we see 110 on a daily basis and the car is coool.. The one thing I never got to was the light bulb for the temp indicator. I took the controller out but could not see any bulbs to be replaced.
What were your symptoms before you replaced the compressor?
 
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