Dan,
'Just set you a comp. clutch schematic. Is it the one you need?
Wilton
----- Original Message -----
From: "Dan Penoff" <lwb...@yahoo.com>
To: "Mercedes Discussion List" <mercedes@okiebenz.com>
Sent: Wednesday, March 14, 2012 7:00 PM
Subject: Re: [MBZ] 300 ACC Issue
I have found a reference to the MAS and what it does in the AC manual, but
they use that darned breakout box to do the troubleshooting.
If I could find a schematic I could figure this out in short order, but
the ones I have been looking at are for older models that use the KLIMA
relay and not the MAS.
Dan
On Mar 14, 2012, at 6:05 PM, Dieselhead wrote:
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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