1987 300D T A/C nightmare - PeachParts Mercedes-Benz Forum

Agar · #1 05-26-2007, 02:19 PM

Any help would greatly appreciated!
I have a 1987 300D T, 185K
The air conditioning was working great, then while driving the system quit every thing, inside fan and the compressor. Fuse 7 burnt, I replaced it and the inside fan now works but the compressor does not at all it does not even come on for second. And it is not blowing the fuse either.
I have read all of the information on the forum I could find and performed the following trouble shooting and I have the wiring print of the ACCU that I am working with.

With the relay removed (engine running) I bridged pin 5 and 7 and the compressor clutch engaged. I also checked the amp draw of the clutch it was 27 amps I know this is bad. However fuse 7 did not blow.
I check for a 10 second ground signal on pin 10 when the center switch is pushed in, there was no ground signal my meter showed open line. This too must be bad.
I checked for a ground on pin 6 no ground.
I checked for a ground on pin 4 no ground.
I checked for a ground on pin 12 no ground.
Pin 1 has a ground.
Pin 5 has 14 volts.

I have also checked the two function switch, it is closed with the engine off and the engine running. Since the 10 second ground signal comes from the push button switch thru the two function switch, with the engine running, the relay installed I jumped blue and red wire going from the switch to the relay to ground, still no compressor engagement. This makes me think the relay is also bad.
I have concluded I must have the a number of failed parts,
first the compressor clutch, two the pushbutton control unit, and the relay (compressor control module).
Can anyone offer any further guidance? I do not wish to spend several hundred dollars shot gunning parts myself, and I am sure a shop would probably throw a bunch of parts at it and finally get the right one thousands later.