The "MAS" relay engages the a/c compressor on that car.

Could be several problems that cause the compressor NOT to come on.

The a/c controller (pushbutton) sends ground signal to that relay thru the low pressure switch on the drier. Checking for that ground signal would be MY starting point.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Thanks!

I see two switches at the drier. One appears to be a traditional A/C low-pressure switch (EDIT: S31) and is ON the drier. The other is green plastic and I think was on a fitting right AT the drier. Would the green one be a temperature switch? (EDIT: The Green one is a pressure switch [S32] that turns on the AUX FAN)

I will find a way to test at the pressure switch. It is good to know I am looking for a ground there from the Climate Controller.

Where is the MAS relay? I may want to examine it for bad solder joints.

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

Hmm... I have 12v on the pins to the pressure switch on the drier. If I ground it there, the compressor and fans will engage.

If this connection's path to ground is directly from the pressure switch on the drier through the Climate Control Unit in the dash, then my CCU has gone bad on me AGAIN!

Is there any chance that there is anything else in the path that could be the problem? If not, then I guess I'd better R&R the CCU...

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)