hi water temp switch

[BillKerler]

Problem arose with intermittent operation of my AC compressor clutch on a 1994 C280. Diagnostic readout of climate control module indicates #26, a high water temperature.
There are 3 water temperature connection devices to my thermostat housing. One has a single green wire, one has two wires (green and brown (neutral)) and the third is a screw on electrical connector.
I'm guessing one of these is the AC interlock switch, one is for an idiot light on the instrument cluster and the 3rd is for the water gauge readout on the cluster.
Does anybody know which is which?
The problem shows up when the car has been parked in the hot sun and then I start it up. Maybe 5 percent of the time I have a problem getting the AC compressor clutch to kick in.
Does anybody have a repair manual showing which is which?

[benzaddict]

The black round 2-pin sensor is for the fuel-injection, the single pole sensor is for the cluster gauge and the blue 2-pin sensor is for the auxilliary fans. The blue sensor is a common failure and should switch to closed at about 108F. You may also want to check your aux fan relays in the fuse box, they have integral fuses on the top of the relays and they blow often.

[BillKerler]

Thank you. This is an intermittent problem.
Isn't my AC compressor clutch pulled in by the overload relay (the silver box relay located near the duo-valve under the black cover on passenger side near the firewall)?
So does the blue water temp switch pull in the aux fan relay (in the fuse box) and contacts from this fan relay get used to pull in the overload relay so that the AC clutch is activated??
I don't have any good electrical drawings of the climate control circuit...any advice is appreciated.
Does the blue water temp switch close its contacts at 180F or 108F as typed above?
The next time I have trouble with the AC compressor clutch, I'll check to see if both cooling fans are on.

[BillKerler]

No sooner did I make the above reply, I went under the hood to the blue water temp switch. When I removed the electrical connector, I saw the green and brown insulation was brittle and mostly gone for 1/2"...the wires were touching, or at least they have the ability to touch (maybe that's why my problem was intermittent).
Man, it is really hot under the hood for these engines. My wire insulation running down to the EGR pump was totally destroyed from heat a year ago. Now this.
Mercedes ought to start using the highest temp insulation wire they can find in the market...
Let's see what happens from here after I fix the insulation.
I would still appreciate anyone with electrical drawings to tell me if the overload relay pulls in the AC compressor clutch. What pulls in the overload relay? Direct from the climate control module in the dashboard? Or from something else? Thanks

[xvvvz]

Bill -

Are you still using the original wiring harness for your car? If so, that year is one of the years that shipped with a wiring harness that is known to go bad with age due to poorly forumlated insulation.

[BillKerler]

Yes, I still have the original wiring harness...and yes it is bad news...especially up front of the engine. No wonder the the head gasket and timing chain cover gasket go bad...the heat is intense. The wire insulation is so very brittle and decayed.
How hard is it to change a wiring harness?? Is that what you did?

[xvvvz]

Fortunately, they had fixed it by my model year. You will find lots of posts about the problem and symptoms it can cause by searching all of the MB forums. Here is one specific to 202's:

http://www.benzworld.org/forums/w202-c-class/1276169-repairing-your-engine-wiring-harness.html

[BillKerler]

Thank you. I will investigate this thread.
As a separate matter, I'm in the market for a 230K and being that you have a '99, have you experienced any transmission problems? Is it worth it to find a'00 model year with the new transmission? Any overall plus or minus comments about your 230K? Thanks.