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2002 X5 4.4i; 1996 sl 320
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Discussion Starter #1
Hello everyone!!!

I went to test drive a 1997 r129 and when i started the AC i noticed that when accelerating it sounds like if a torrent of air was coming out of the widshield vent... Does someone know why this could happen???
 

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2002 X5 4.4i; 1996 sl 320
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115 Posts
Discussion Starter #2
Thanks sl5001997 !!!

Absolutely ¡!! It sounds like a jet engine!!! Well anyway I loved the car, I guess I am buying it tomorrow after a Benz dealer inspection.
 

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Greek God of the R129
SL500-500SEL-190E
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Check the cabin filter if it's in there.
That is if you have not a jet engine. Haha.

Regards.
aam.
 

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Departed 1998 SL500 (and the Pano is in Bogota)
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Since you are having a MB Dealer to do Inspection tomorrow, just bring up that 'noise' subject and have them take a look into the blower in the cabin air filter area.
Chances are it has a dirty filter and the blower had to work extra hard, and it was complaining (made noise).
 

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2007 CLS 550, 1998 Harley Road King, 2011 F-150 EcoBoost, '65 Shelby Cobra
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I have a slightly different problem or at least I think it is a problem. When I accelerate moderately to hard, I loose the AC air coming out the vents. No "jet" noise, just no air at all. As soon as I let up and return to normal driving or accelerate gradually, the AC works perfectly. I have brought this up before in the forum, but no one seems to be able to give me a satisfactory explanation. At first I thought it was normal and perhaps MB shuts down the system to assist with acceleration. That really didn't make a lot of sense, but there are plenty of other strange things MB does.

Now I am thinking it could be a vacuum problem. The air handling is directed by vacuum to the internal vents. Under moderate to heavy acceleration, the available vacuum from your engine is greatly reduced. Maybe there is a bad check valve in the system. In your case, the vents might go the the defrost position??? In my case, I have no idea what happens to the air. :confused:
 

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2000 Obsidian Black Metallic Mercedes SL 320 V6
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RoadKing in various cars I've had say starting from a 1995 Lancia K Turbo 16V (Italian sedan car comparable to an E Class not imported in the US) the Engine ECU used to shut down the A/C compressor under heavy acceleration but not the air flow so I think you might have a vacuum pressure problem somewhere because that behavior is not normal in my opinion. I'm sorry I can't provide either a decent solution but I can confirm that it's not normal unless Mercedes decided to assist acceleration in this strage way but to me it seems unlikely.

Cheers.
 

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1991 500SL
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51 Posts
Road King, I had the exact problem with my AC on a 91 500 SL. On hard acceleration I would loose the air, it turned out to be a loose belt. Hope this may help.
 

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RoadKing in various cars I've had say starting from a 1995 Lancia K Turbo 16V (Italian sedan car comparable to an E Class not imported in the US) the Engine ECU used to shut down the A/C compressor under heavy acceleration but not the air flow so I think you might have a vacuum pressure problem somewhere because that behavior is not normal in my opinion. I'm sorry I can't provide either a decent solution but I can confirm that it's not normal unless Mercedes decided to assist acceleration in this strage way but to me it seems unlikely.

Cheers.
I am sure you are correct. The problem for me is that with the age of my car, the only thing that scares me more than the electrical system is the vacuum system! :eek: The deterioration I had to correct on vacuum lines in the engine compartment has me scared to death to dig into the rest if the vacuum system for fear of cracking something amd making it worse.

My apologies to MaxR129 for hi-jacking your thread. I have complained of others doing the same thing and here I go! I have a feeling, however, that we are looking at the same problem. Perhaps a different vacuum line or a different controler fault, but very similar. Good luck.
 

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MB SL600, MB 380SE, Suzuki Grand Vitara, 38' Chris-Craft, Volvo V70XC, and my own two feet...
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RoadKing in various cars I've had say starting from a 1995 Lancia K Turbo 16V (Italian sedan car comparable to an E Class not imported in the US) the Engine ECU used to shut down the A/C compressor under heavy acceleration but not the air flow so I think you might have a vacuum pressure problem somewhere because that behavior is not normal in my opinion. I'm sorry I can't provide either a decent solution but I can confirm that it's not normal unless Mercedes decided to assist acceleration in this strage way but to me it seems unlikely.

Cheers.
+ 1
 

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1991 500SL
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There is supposedly an engine speed sensor connected to the A/C compressor that shuts off the compressor under hard acceleration, to give you that extra power when you need it. It engages again when the acceleration stabilizes.

However, as mentioned above it should only cut the compressor not the blower motor, so you should still get air.
 

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2000 Obsidian Black Metallic Mercedes SL 320 V6
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Honestly, but it's my personal opinion, I've never liked that feature since I met it in that car I mentioned above. I mean, why you should need those additional 10 BHPs in a car that has 200 or more BHPs ?
I find it useless in our cars since the difference is barley noticeable and I don't like the smell coming from the vents when the compressor shuts off.
Anyone agrees ?

Cheers.
 

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Greek God of the R129
SL500-500SEL-190E
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Roadkink.
Mike the vacuum reservoir for the A/C is located in the left fender well.
I have mentioned it before, sometimes it leaks.
It is the one with two balls, remember? Hahaha ;)
Regards.
aam.

Mick, if the A/C stops for a second or two you are not going to feel it.
Hmmmmm.
Maybe I am numb and I don't even know it?
 

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97SL500R129, 01ML320W163, 94E320W124 & 93500EW124
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I mean, why you should need those additional 10 BHPs in a car that has 200 or more BHPs ?
Cheers.
I think it is not the additional HPs they are after. But, to take off the extra load during rapid acceleration to prevent the serpentine belt from breaking. The (inertia) force during rapid acceleration is greater than during normal (smooth) take off. Thus, the ac compressor is turned off during rapid acceleration.
 

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2000 Obsidian Black Metallic Mercedes SL 320 V6
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I think it is not the additional HPs they are after. But, to take off the extra load during rapid acceleration to prevent the serpentine belt from breaking. The (inertia) force during rapid acceleration is greater than during normal (smooth) take off. Thus, the ac compressor is turned off during rapid acceleration.
Yeah that too probably but since I only started noticing this kind of behavior in a 1995 car I wonder why they didn't it before or at least how they solved the problem before. Probably downising internals to save money from then on?
As for aam comment, when I floor it it's not only for a second or two lol ;).

Cheers.
 

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97SL500R129, 01ML320W163, 94E320W124 & 93500EW124
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Yeah that too probably but since I only started noticing this kind of behavior in a 1995 car I wonder why they didn't it before or at least how they solved the problem before. Probably downising internals to save money from then on?
Cheers.
Early cars use several fan belts for each components (water pump, AC compressor, Alternator,air pump and etc.) Usually the ac compressor has its own belt. So, loosing the ac comp belt would not immobilize the car. On later cars, when one serpentine belt for all those components became the norm, it became necessary to design a system to enable the single belt to to handle such condition as rapid acceleration without breaking.

Also, you are right when you say "downsizing to save money." They were able to eliminate several belts and pulleys.
 

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Outstanding Contributor
'03 SL500, '03 SL55, '97 SL320, (2) '91 300SL, (2) '91 500SL, '00 S500 -- all for sale
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There is supposedly an engine speed sensor connected to the A/C compressor that shuts off the compressor under hard acceleration...
The compressor does not disengage under acceleration on an R129. It does disengage if the speed sensor detects that the compressor shaft has frozen because this would imply that the serpentine belt is slipping on the pulley.
 

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2000 Obsidian Black Metallic Mercedes SL 320 V6
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The compressor does not disengage under acceleration on an R129. It does disengage if the speed sensor detects that the compressor shaft has frozen because this would imply that the serpentine belt is slipping on the pulley.
Bob, neither on post 1999 cars?

Cheers.
 
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