Automatic Climate Control

[BillKerler]

I have a '94 C280 with 183K miles on it. At 100K, the wiring harnesses were replaced per M-B guidelines.
I developed intermittent A/C problems along with intermittent heating in the economy mode.
What a pisser.
To look at my wiring harnesses, the cloth type black tape wrapped around individual harnesses looks great. Take a sharp razor blade and cut through the tape and you will discover horrible wire insulation problems...engine heat has disintegrated the insulation and bare wires touch...intermittently.
My automatic climate control (ACC) has diagnostics...go to Programa.com and the instructions on how to call up the diagnostics is given. (Instruction 20785 for my '94 C280)
I got temp sensor 25 and 26 as the reason why the A/C was not working. I thought there were 2 temp switches...silly me, it turns out A/C ACC temp sensor R1075-26553 mounted in the water pump housing right under the thermostat housing, sends out a signal and as water temp progressively increases, from 100 C to 108C, temp trips 25 and 26 occur (26 is the 100 C trip). This kills the A/c from working.
As I peeled apart the wiring harnesses I was aghast at the condition of the wire insulation...or lack thereof. I piece mealed new insulation using Scotch black wire tape. I put old radiator hoses I keep around for new conduit heat protection of these wires.
My temp temp sensor was bad...my wire insulation was worse...I don't have the foggiest idea on how the car even worked at all. But the problem got fixed.

[strictlyspeakin]

I remember searching for a second temp sensor that you were looking for. I never got back to you because I couldn't find it on the drawings anywhere. Now it makes sense why I couldn't.

Thanks for posting back about it and what you did to fix it.


What is the url for programa.com? The one I tried was some squatters site.

[BillKerler]

Go to search and type in:
A/C problem
Go to 2nd page, A/C problem by Boomin Benz, repairs, 11/1/2005.
Nenad gives you the full code process
Here's a question, now that the A/C is fixed, how about the temp sensor for the fuel injection ECU (on the side of the water pump housing).
With mine, I never get a 1000 to 1200 rpm warm up and then idle speed dropping down to 600 rpm when engine is warm.
I always got 600 rpm. I live in California and no real big deal.
When I fixed wire insulation on wires to the ECU temp sensor, voila, I get fast idle on warm up...the car has a lot more pep as the coolant warms up.
On my OBD II port hook up to my Actron readout device, I never got a code saying this sensor was misbehaving.
These temp sensors are variable resistance only with temp changes. They give great resistance readouts when cold...they fail in the hot mode...check resistance only when engine is hot. If you get a momentary 10K ohm reading or something and then quickly your digital ohm meter goes to infinity, it's the sensor being bad.

[OzC36]

I'm confused. Here are two temperature sensors. One in the air intake and another one to measure coolant temperature:

http://www.autohausaz.com/search/product.aspx?sid=evnfvh552v51zn55fnhbzh45&makeid=800016@Mercedes&modelid=1195512@C36&year=1996&cid=temperature@temperature&gid=4740@Temperature%20Sender%20Switch

Here is another temperature sensor that is described as air-conditioning OFF emergency switch and being located in the intake manifold:

http://catalog.autohausaz.com/autohausaz/detailw.jsp?sid=evnfvh552v51zn55fnhbzh45&partner=autohausaz&product=R1075-26553

Are you talking about yet another temperature sensor?

I also have the low idle RPM start problem....

Cheers,
OzC36

[BillKerler]

I spent a month trying to figure out the ad your thread leads to.
First, note the ad says 130 C temp in the air intake manifold. If your air intake manifold ever gets up to a 130 C, run away from the car, it's on fire.
Second, I actually went to Behr via the internet and with no German language skills believe me, communication was difficult. There seems to be a translation problem...Behr was referring to the manifold on the water pump intake manifold. This temperature switch is made to work in a liquid...not in an airstream. Look at the length of its brass sensing end.
But undaunted by all that, I still ripped apart my intake manifold in search of this mysterious 2nd switch for shutting down the A/C. Nothing is there. There is a vacuum connection on the air plenum manifold and there is a sensor with 3 wires for my USA made car. A green wire goes to the ECU and 2 black with red stripe wires...one of these black wires goes down to the electric EGR air pump and the other goes to the instrument cluster. Just to be sure it had no effect on the A/C, I disconnected the black with red stripe wire to the cluster and immediately got check engine light with error code 400, EGR malfunction.
No, the Behr A/C shutoff temp sensor is a variable resistance device which at one resistance near 100C (somewhere north of 5K ohms) trips the A/C and brings on the auxiliary cooling fans at low speed (about 8 VDC to the fan motors)...this is ACC module trip #26. Later, about 108C, you get trip #25 on the ACC module which makes the auxiliary fans spin even faster (a full 12 volts to their fan motors).
I'm without drawings or manuals, but this is what I have come up with.
Nice car, screwy electrics. No wonder they lost the war.

[BillKerler]

Forgive me, I did not address the air temp sensor in the crossover plenum of the air ducting. The wires for this sensor go to the ECU for fuel injection. This sensor has nothing to do with A/C that I can see. As air temp changes, air density changes, and air/fuel ratio gets affected. This air device corrects for this.

[BillKerler]

As for your low rpm as the cold engine warms up, take a sharp razor blade edge and cut through the tape wrapped around your motronic water temp sensor on the side of the water pump housing. Remove the black cover for the conduit trough (which means the black air plenum crossover duct needs to be removed) as you need to trace the wire back towards the firewall where the ECU is mounted. You will be amazed in how many places your wire insulation has rotted away from heat and bare wires are touching. I used a lot of 3M Scotch black electrical tape and new shrink tube around both wires to get rid of the shorts. Use an ohm meter to check when the 2 pins of the connector no longer show a short condition to know when you are done. Careful though, bare wire might be ever so close when the engine is cold and stationary, versus when it heats up and bouncing along down the road. What is isn't a short in your garage can become a short out on the road. That's why I ripped apart the black tape conduit...I got virgin wire about 10" before reaching the firewall. I had about 40" of length of sheer disaster with insulation problems on the wire. I hope the guy who selected this wire for Mercedes rotts in hell.