1990 300SE No activation of A/C Compressor - PeachParts Mercedes-Benz Forum

BENZ TEK · #1 06-13-2007, 09:39 AM

Hello all!!
I have a 1990 300SE in the shop because the A/C compressor will not engage. I noticed that this car does not have the traditional klima relay. I think all of the processes go thru the MAS relay in this model. I am trying to find out if I am getting a signal from the A/C push button to activate the compressor but don't know what pin in the MAS relay (if thats how you check) I am suppose to check for activation. Any help would be appreciated!!

brewtoo · #2 06-13-2007, 10:35 AM

There was a discussion of this in the last few days. A search should find it.

Here it is:

Long and Covoluted intermittant A/C Problems with '88 300TE

BENZ TEK · #3 06-13-2007, 10:49 PM

Quote:

Originally Posted by brewtoo

There was a discussion of this in the last few days. A search should find it.

Here it is:

Long and Covoluted intermittant A/C Problems with '88 300TE

Thanks for the help BREWTOO but they are talking about a car with a Klima relay which in 1990 I believe that they incorporated it into the MAS Relay on the 300SE. The Mas relay is located where the fuel pump relay and Klima relay was located on earlier versions. It sits right beside the overvoltage protection relay. I can't be sure tho. Maybe they moved the relay to a different location all together. Thanks again for the help!!

wscheffer · #4 06-13-2007, 11:45 PM

Did you check your pressure switch on the dehydrator? If this is faulty your compressor will not engage.

jbaj007 · #5 06-14-2007, 12:26 AM

Discusses MAS control of A/C and the use of impulse counter in 1990+ models.
http://www.continentalimports.com/ser_index.html doesn't link to article directly. Go to magazine articles..last article on the page.

BENZ TEK · #6 06-14-2007, 09:51 AM

Quote:

Originally Posted by wscheffer

Did you check your pressure switch on the dehydrator? If this is faulty your compressor will not engage.

Yes I did and that checked out fine!! Thanks for the help!!

BENZ TEK · #7 06-14-2007, 10:16 AM

Quote:

Originally Posted by jbaj007

Discusses MAS control of A/C and the use of impulse counter in 1990+ models.
http://www.continentalimports.com/ser_index.html doesn't link to article directly. Go to magazine articles..last article on the page.

Thanks for the very useful information. I didn't find what I needed to solve the problem but I did find some of the charts I've been looking for!!

raymr · #8 06-14-2007, 03:09 PM

Are you checking voltage on the wire going to the compressor?

BENZ TEK · #9 06-14-2007, 06:21 PM

Yes. I have no voltage to the activation wire for the compressor clutch.