[W126 Coupe] Air Recirculation Switch (*Thud*)

[Dawid Loubser]

Hi All,

Though I am reasonable happy with my car's climate control (the  
drivers' side seems to always be a bit "colder"
than the passenger side, but otherwise leaving it on 22ºC always  
keeps the interiour comfy, regardless of
exteriour temperature) I have one small problem:

Most of the time, when I hit the recirculation switch
(e.g. because I'm stuck after a minibus taxi with white exhaust smoke  
pouring out of it) it engages after
about 1 second with a loud (sometimes very loud) thud. It sounds  
either like the vacuum pressure which does this,
slowly mounts and then suddenly kicks in, or maybe there's some  
resistance?

It's clearly on the passenger side (left side). I haven't opened  
anything up yet to look, but does anybody have
any experience on a similar problem? Everything works fine, it's just  
annoying. It's also gotten worse over the past
3 months. Also, thud loudness is about the same, regardless of fan  
being switched on 1, 2, 3 or 4 (so it doesn't seem
to be the air movement itself suddenly "catching on" to the thing  
that closes, sucking it closed).

It's not a mechanical-sounding "thud" - but sounds similar to the  
sound when you accidentally suck a large object
onto the hose of an operating vacuum cleaner (violently closing off  
the air flow).

regards,
Dawid