[W126 Coupe] Air conditioning diagnosis II

[Dick Spellman]

Hi Fred:

The clicking noise you checked is at the monovalve?  Or is it up behind 
the dash, say to one side of the ACC push button control unit?  If it's 
the latter then the pushbutton control unit itself may have a bad pin 
connector or the pushbutton control needs to be replaced as I have done 
on two MB's.

The clicking is typically the vacuum switching valve up to the side of 
your acc pushbutton unit and it get's to clicking and so on when the acc 
unit drops voltage to the switching valve in rapid fashion sort of like 
flicking a light switch rapidly at home.  This is a sign that the push 
button unit needs some attention and with the absence of a continuous 
voltage to the compressor relay you get no ac as you have described.

Of course, checking the charge on the refrigerant circuit, checking that 
air is flowing from the correct outlets (vacuum elements) and checking 
the vent temps when the AC is blowing cold once again will tell you if 
other things are in need of service as well.

Regards,

Dick

FREDERICK AULD wrote:

> I hope i'm not stealing Dan's thunder on the the a/c diagnosis issue, 

> but could i also mention an a/c problem on my 500 SEC ?

>  

> My 1986 500SEC (no airbags) has also developed an a/c fault... it was 

> working fine (very cold) until one day recently, when the compressor 

> would not activate when hitting the a/c button.... before then, I had 

> noticed that it was taking more than few seconds for the compressor to 

> activate after hitting the a/c button, but didnt think much of it.  

> The system was regassed less than six months ago, and each time it's 

> regassed, the service agent says that there are no leaks in the system.

>  

> I've also noticed that my monovalve is getting increasingly noisy... a 

> regular clicking noise can be heard at idle, but this has been 

> happening for ages now without any apparent adverse affects...  would 

> this be related to the a/c problem?  I suspect not given the sudden 

> nature of the compressor calling it quits.

>  

> I also checked the fuse, which seems ok.  Belts seem ok, but are due 

> for replacement.

>  

> The small red light on the a/c switch stlll illuminates.

>  

> If things do get warm over here in the UK (yes, that's possible), i'll 

> jump into the (new, yah !!) 560 whose a/c seems to work ok.

>  

> Cheers, Fred.

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