Read #2 and #3 here
http://www.w124performance.com/service/W126/Index/Misc.htm
I think you are right, that the wire from the low pressure switch to
the comp is the clutch power wire. With it off at the comp, measure
resistance of the terminal on the compressor to ground. Open or near
0 resistance means the coil is bad. (obviously) I don't know what
the resistance should be, probably 1.5 to 3 ohms. is a good coil.
You could also have someone turn on the AC while you are measuring
the voltage of that wire to ground. It should show 12v for a short
time, until the system detects the pulley is not turning.
It is possible the "everything" relay replaced the Klima. Or maybe
they moved the Klima on that model.
OK, guys, pile on. I'm in unfamiliar territory here, and could
really use some direction:
1992 300E 2.6, complaint is AC compressor won't come on.
Original complaint was that the #7 fuse was blowing, killing all ACC
related functions. Fuse was replaced, and now ACC functions as
expected, that is, fan speeds, doors, heat/defrost, etc. Everything
works but the AC compressor.
I shorted out the low pressure switch with no result. Checked for
power in the harness to the low pressure switch in reference to
ground and got nothing.
This model has a MAS relay which may or may not play a part in this,
but I don't have a schematic, so if anyone does, I would really
appreciate you forwarding a copy to me, as that would make my life
significantly easier in identifying the problem.
If I pull the MAS relay while the car is running the engine dies, as
I would expect. Since it's supposed to interface with all sorts of
things like the fuel pump and other goodies, it appears to be
working as intended, as everything else on the car works perfectly.
I have to believe there is a failure in getting a signal to the
compressor clutch, but without a diagram I'm swinging in the
proverbial wind. I would put B+ to the clutch, but I'm unsure of
what wire is which, and I don't want to smoke the speed sensor in
the process.
From what I can glean, it appears that power comes in, goes through
the low pressure switch, and then on to the compressor clutch.
That's an educated guess based on what I am seeing, but I'm not
tearing harnesses apart, either. There are three wires going to a
connector on the top of the compressor, two of which go off in a
separate harness that heads up under the air cleaner. The remaining
wire goes to one side of the low pressure switch. I am assuming the
two that head into the engine harness are for the speed sensor.
Dan
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