Air release noise (pssst) whenever coming to a stop
Member
Joined: Sep 2017
Posts: 129
Likes: 117
From: Spring, TX
'07 S65 '05 SL65 '07 GL450 '03 SL55 (sold)
Thanks Dennis. I wasn't aware the compressor had an air filter until I searched older threads on the hissing noise and learned about the air filter in this thread. I'm going to disconnect the air filter hose from the compressor and identify where the noise is coming from and report back here. Also, when I replaced my air compressor, the air filter line was damaged exactly like in this video. I figured the air hose ran up into the wheel well somewhere and really didn't give it much thought. So I cut the damaged portion off and fit the air hose back onto the new compressor when installing. Looking back, having the broken air filter hose at the inlet of the air compressor exposed the compressor to unfiltered air and likely contributed to the compressor's failure. Also, as noted in the video, the damaged hose allowed unfiltered air and debris to enter the compressor over a number of years and may have damage the valve block as well. While I don't have any codes for the Airmatic system that point to the valve block, I'm curious if the valve block seals are possibly damaged and are contributing to the problem. If removing the air filter hose stops the loud and long hissing, then I'll know the air filter hose is the problem, or one of the problems. I'm planning to buy the replacement filter noted in the video. Once I get it fixed, I may end up doing a comprehensive write-up to help folks diagnose these issues. During my searching, it seemed like 95% of the time it was defective air bags. I'll report back here once I learn more.
Unfortunately, he doesn't say in the video what ended up fixing the problem..
Unfortunately, he doesn't say in the video what ended up fixing the problem..
Senior Member
Joined: Oct 2017
Posts: 302
Likes: 43
From: Saint Louis
2010 GL550 | 2020 S560
Thanks Dennis. I wasn't aware the compressor had an air filter until I searched older threads on the hissing noise and learned about the air filter in this thread. I'm going to disconnect the air filter hose from the compressor and identify where the noise is coming from and report back here. Also, when I replaced my air compressor, the air filter line was damaged exactly like in this video. I figured the air hose ran up into the wheel well somewhere and really didn't give it much thought. So I cut the damaged portion off and fit the air hose back onto the new compressor when installing. Looking back, having the broken air filter hose at the inlet of the air compressor exposed the compressor to unfiltered air and likely contributed to the compressor's failure. Also, as noted in the video, the damaged hose allowed unfiltered air and debris to enter the compressor over a number of years and may have damage the valve block as well. While I don't have any codes for the Airmatic system that point to the valve block, I'm curious if the valve block seals are possibly damaged and are contributing to the problem. If removing the air filter hose stops the loud and long hissing, then I'll know the air filter hose is the problem, or one of the problems. I'm planning to buy the replacement filter noted in the video. Once I get it fixed, I may end up doing a comprehensive write-up to help folks diagnose these issues. During my searching, it seemed like 95% of the time it was defective air bags. I'll report back here once I learn more.
https://www.youtube.com/watch?v=9Z0kydl9aak
Unfortunately, he doesn't say in the video what ended up fixing the problem..
https://www.youtube.com/watch?v=9Z0kydl9aak
Unfortunately, he doesn't say in the video what ended up fixing the problem..
While reinstalling my bumper about a year ago after retrofitting my headlights my hose was the same as the one in the video. I cut the hose and reassembled the clamp. It made the hissing sound much much quieter. However, I feel it may have come off again because its loud again. Im just going to order a new hose from FCP Euro and install.
Member
Joined: Aug 2019
Posts: 173
Likes: 36
2014 GL550; 2010 GL450
I've owned my '07 GL450 since new. It currently has 190K miles. I replaced the air compressor and front struts about 1.5 months ago. No codes in the suspension system with MBII and all of the struts are proper height and not losing air. Been noticing a louder and longer hissing sound lately. It's usually when the last door is shut when parked and then this loud and prolonged "TTTttttttsssshhhhhTTT' sound. Ever since it was new, it's always had the normal "Phstt" sound sound when closing a door when parked. But ever since the new compressor was installed, the sound has become much more pronounced and longer. I found this thread from a few years ago and the link in the post above describes a damping mat that was used in the vicinity of the Air Compressor Filter Assembly. Couple of questions: Has anyone ever heard of this damping mat? Does it work? (I could not find it on the internet). Is the air compressor filter hose also the discharge hose that makes the noise when closing the door and/or is there a separate discharge hose/port on the air compressor. If the air compressor filter hose is also the discharge port, will replacing the air compressor filter help to alleviate the loud noise upon closing the door? Btw, I don't think the air compressor filter has ever been changed. I know it's supposed to be a maintenance item. I just haven't ever replaced it. This is the car's third air compressor (this latest one is a free replacement from Arnott and I did install the new relay that came with this latest compressor). This seems to be an occurrence across many different airmatic models, and after searching I still haven't found a definitive answer. Any thoughts are appreciated!
MBWorld Fanatic!
Joined: May 2015
Posts: 1,932
Likes: 291
From: Allentown, PA
'08 GL 320 CDI
Mine releases air even when driving or coming to a stop while driving. I've never figured out why. I asked a service adviser once whether it's normal and his answer wasn't straight forward. He's seemed to suggest that it's normal for older pump after he asked if my pump had ever been replaced (I don't know that it has at 115K but I haven't owned it since new). I replaced the filter and front air bags a couple of months ago and the hose looked OK then. If you ever find out what's going on with yours perhaps it can shed some light on mine.
MBWorld Fanatic!
Joined: Aug 2003
Posts: 8,882
Likes: 1,212
From: In my garage
E55, GLS450, GL63, GLE350
Senior Member
Joined: Aug 2018
Posts: 409
Likes: 121
From: Kelowna, BC
08 GL320 CDI
Mine always makes that sound when I lock the door. I always assumed it was just the vehicle leveling itself or something. I also hear it while driving sometimes, again, assumed it was the system trying to level its self between all the wheels.
I remember reading somewhere that the vehicle will lower slightly to allow easier access to the vehicle.
I remember reading somewhere that the vehicle will lower slightly to allow easier access to the vehicle.
Senior Member
Joined: Apr 2023
Posts: 314
Likes: 34
Mercedes gl450
The vehicle also lowers at highway speed and raises at lower speed. So, if this happens when you come off a highway, that could be it. Although it should be taking in, not releasing, air then.
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Senior Member
Joined: Apr 2023
Posts: 314
Likes: 34
Mercedes gl450
Mine always makes that sound when I lock the door. I always assumed it was just the vehicle leveling itself or something. I also hear it while driving sometimes, again, assumed it was the system trying to level its self between all the wheels.
I remember reading somewhere that the vehicle will lower slightly to allow easier access to the vehicle.
I remember reading somewhere that the vehicle will lower slightly to allow easier access to the vehicle.
MBWorld Fanatic!
Joined: Jan 2010
Posts: 3,114
Likes: 782
NGL450 w/EORP, S550
The compressor is constantly taking in air when the car is running. It has a release valve to prevent it from over-pressurizing, So, it would be normal to hear occasional air release while driving (although most of the time, that noise is drown out by other normal noises on the road).
A constantly running compressor is an indicator that somewhere in the system there is a leak, and that leak created increased demand for pressure.
Senior Member
Joined: Apr 2023
Posts: 314
Likes: 34
Mercedes gl450
Not quite. The compressor runs only when commanded to fill the central pressure reservoir when it falls below a pressure threshold.
A constantly running compressor is an indicator that somewhere in the system there is a leak, and that leak created increased demand for pressure.
A constantly running compressor is an indicator that somewhere in the system there is a leak, and that leak created increased demand for pressure.
MBWorld Fanatic!
Joined: Jun 2010
Posts: 2,755
Likes: 628
From: Emmett, ID, USA
2007 GL450
The compressor is constantly taking in air when the car is running. It has a release valve to prevent it from over-pressurizing, So, it would be normal to hear occasional air release while driving (although most of the time, that noise is drown out by other normal noises on the road).
I actually had an early Campbell Hausfeld tankless air compressor that ran like that. It was a great relief to add a pressure switch. It also probably helped ensure the pump had a reasonable lifetime.
Senior Member
Joined: Apr 2023
Posts: 314
Likes: 34
Mercedes gl450
Nonsense. The pump cycles exactly as @Max Blast described.
I actually had an early Campbell Hausfeld tankless air compressor that ran like that. It was a great relief to add a pressure switch. It also probably helped ensure the pump had a reasonable lifetime.
I actually had an early Campbell Hausfeld tankless air compressor that ran like that. It was a great relief to add a pressure switch. It also probably helped ensure the pump had a reasonable lifetime.
Airmatic pressure relief valve problem
MBWorld Fanatic!
Joined: Jan 2010
Posts: 3,114
Likes: 782
NGL450 w/EORP, S550
the audible whoosh is venting of excess pressure anywhere from the central reservoir, or in the compressor chamber back through the intake tube. It occurs when the Reservoir says it is full and the residual pressure is then vented overboard through the intake tube.
this is merely speculation, but I imagine they did it that way to clean the filter regularly with a blast of pressurized air from the inside.
if you have a ruptured air intake tube for a missing filter, I would imagine that wish is much louder than in a properly functioning system.
not to add another noise description to this thread, the what I would call air movement sounds, that aren’t wooshes but sound more like a high frequency flute being played - they are individual airbag pressurization adjustments where the excess pressure or lack there of is either distributed to or taken from the central air, Reservoir to the individual air springs at each wheel.
Last edited by Max Blast; Jul 15, 2023 at 12:13 PM.
MBWorld Fanatic!
Joined: Jun 2010
Posts: 2,755
Likes: 628
From: Emmett, ID, USA
2007 GL450
or the compressor exceeding its run time after the desired pressure threshold has been Met. It’s quite possible to significantly over pressurize the system even with a couple of seconds of extra run time… The compressor is capable of making 16 bars in less than 30 seconds so a few extra seconds of runtime could easily resulted in significant overpressure, that Hass to be vented overboard. That extra runtime could be accounted to delays in the sensing system or dynamic loads.
Hass is the main type of avocado grown in North America. Autocorrect funny.
the audible whoosh is venting of excess pressure anywhere from the central reservoir, or in the compressor chamber back through the intake tube. It occurs when the Reservoir says it is full and the residual pressure is then vented overboard through the intake tube.
this is merely speculation, but I imagine they did it that way to clean the filter regularly with a blast of pressurized air from the inside.
this is merely speculation, but I imagine they did it that way to clean the filter regularly with a blast of pressurized air from the inside.
Perhaps it is a regen cycle for the dryer, which presumably is silica gel and occasionally needs to be heated, with the damp air them pushed out - but it would make more sense to do this with a slow passage of air, not fast.
Maybe it's both.
I don't think it is venting "excess" pressure from the reservoir; the system only ever brings the reservoir pressure up to nominal, and I'm pretty sure air from the springs is never routed to the reservoir. It is only pump to reservoir and reservoir to springs, except when raising the suspension, in which case the pump simultaneously pushes on all four corners.
if you have a ruptured air intake tube for a missing filter, I would imagine that wish is much louder than in a properly functioning system.
not to add another noise description to this thread, the what I would call air movement sounds, that aren’t wooshes but sound more like a high frequency flute being played - they are individual airbag pressurization adjustments where the excess pressure or lack there of is either distributed to or taken from the central air, Reservoir to the individual air springs at each wheel.
not to add another noise description to this thread, the what I would call air movement sounds, that aren’t wooshes but sound more like a high frequency flute being played - they are individual airbag pressurization adjustments where the excess pressure or lack there of is either distributed to or taken from the central air, Reservoir to the individual air springs at each wheel.
I would guess the passages to the springs are small, while the passage from the pump and to the reservoir is large. No point in putting impedance in the path of the pump's output!
