S500 sigh

[Suki]

Hi, My dad has an w220 s500.?
Recently the air suspension went which resulted in the common change of the compressor and relay.
However a strange thing has happened
Before we got the parts replace the car used to sigh after you locked the car (following a car journey).
What I mean is the pressure appeared to release from the front suspension resulting in the car lowering by an inch or so. When you start the car the front suspension would rise.
Following the replacement of the parts (by Merc) the no longer occurs.
Does anyone know if there was a fault in the car previously or are Mercedes spinning me a yarn by saying the car should never sigh?
Thanks in advance
Suki

 

[television]

Very hard to answer exactly,, some of these relays could stick and maybe making the Hiss,,I will take a look when I trn on next time

 

[Xtractorfan]

I.ve heard my car do it on occasions, and now I never notice, But i'm sure it still does. I always put mine down to the fact the car was glad to get home safe..... touch wood, the only problem i had with mine was the compressor rivets corroding and the darned thing fell from its mounts..
I do believe that the suspension settles after driving and releases any built up pressure from the pipes..

 

[Suki]

Malcolm, thanks for your prompt answer. The sigh is definitely a release of pressure and not a relay.
Does anyone know of any merc documentation reporting that this should/should not happen? I can not find any reference to it in any literature I have
Regards
Suki

 

[television]

When relays stick or become faulty, they enable the pump to misbehave, and this is where the relay bit comes in, I will take a look and see if this is listed

 

[BlackC55]

The hiss is the valve releasing air back through the pump's drier to help reduce the moisture content entering the pump.