Freeze out in the 560
 

Yesterday coming back from the So Cal GTG, even though outside temps were well over 100*F, I was freezing in the car. The problem was that the ACC never kicked to low speed fan, although I was able to just set it to low and not be blown out, the temp never stabilized at comfortable (but I do like it cold, but this was too cold :eek: ).

Today I tested the interior sensor by using a small piece of tissue paper over the grate next to the interior light, the paper kind of stayed, but I think it was due to static rather than air draw. I pulled the light assembly and checked out the unit visually. I don't see any small fan in there but did see a blue resistor (or some piece of electrical gadgetry).

Is the fan in this unit or is it located at the other end of the tubing? The tubing is rubber, like large vacuum line not the foam type the 123 owners have to replace. I'd like to get the ACC working correct again before heading to Laughlin this weekend.

While eating dinner I thought about this and decided to re-run the tissue test. I started with the car off, to see if static was what held the tissue in place - I couldn't get it to stick. Then I started the car and kicked on the ACC and the paper stayed against the grille, when I shut the car off the paper fell to the floor. That tells me the fan is drawing air across the sensor, so the sensor must be dead or dying.

I looked through FastLane but couldn't find the part, did a search in PartsShop for "thermistor" and came up empty. Anyone know the part number for the interior temp sensor on a 560SEL?

I would think it's not likely to be the sensor, but it is easy to check. Measure the electrical resistance at room temp. Then heat it up to 90 degrees or so and measure it, then stick it in the refrigerator to take it down to 40 degrees or so and measure it again. If you can see the resistance change with temperature, the sensor is probably OK. Climate control manual probably has a table showing what the resistance should be at any given temperature (Centigrade, of course). If it's like a 123, sensor goes to the acc control unit. 123 acc manual shows how to test the controller with a special tool, but, by reading between the lines you can figure out how to test it manually.

P.S. Smoke from a cigarette makes a good quick check to see if the hose is drawing air. Might be easier than the paper method.

Thanks Paul, now I'm not sure what's up, everything was working fine this morning.

Did a little reading in the climate control manual last night and found the Ohm values for various temps, so I plan on testing. This morning when I headed to work, I had the system set to Auto, and it started blowing hi fan and the fan promptly started slowing in stages. Outside temp was 62*F, dial set to about 20*C and the system put out warmed air until reaching the dial setting, then began softly blowing comfortable air with the A/C thermometer reading ~70*F.

Only thing that changed, other than my removing the sensor to look at it, was I cleaned it out by blowing thru it. There was a fairly thick layer of fine dust coating the inside. The resistor (or whatever makes up the sensor) was also coated in this dust and it took a shot of compressed air to get clean. Perhaps the dust was acting as insulation??

We'll see how well everything works this afternoon when the temps are in the 100's.

This afternoon was HOT. I got in the car and turned the A/C down cold, not all the way to MIN but close. The fan never came off HI. The interior got nice and cool, but the fan kept blowing HI. After getting home I played with the dial, and I found that by setting to at least a shade over 18*C, the fan would start to slow in a matter of minutes anything colder and it stayed at HI.

Now I'm wondering if there isn't some sort of default to keep the fan on Hi when the dial is turned colder than a specific point. Anyone know?

Time to read some more in the climate control section.

After reading your post last night, I experimented with my a/c today.

If I turn the dial all the way to its coldest position, the fan remains on Hi.

If I set it to a less cool temperature, really any temp less than all the way, the fan will modulate its speed.

Thanks Paul. Perhaps I have a slightly miscalibrated dial. I was enjoying the super cool air, but the gale force wind was making it a mite uncomfortable ;). I guess all is normal.

On a side note, I also played with the rear seat adjustment. Thinking the kids had played with the buttons, yet again, and not knowing if a fuse or switch had gone bad, I played. I found that with the door open the seat wouldn't adjust but with it closed the seat works fine. One of two things; a safety to keep the seat from adjusting with the door open or a faulty wire in the harness that open when the door is open.

I was thinking that too Mike because my rear seat does the same exact thing...maybe it is some sort of feature. I thought it only worked sometimes until I held the switch and opened the door and started to move. I was then thinking there was a short somewhere but you're the second person besides myself that has noted this. Does anyone know if this is a "feature" to stop you from being able to move the rear seat if the door is ajar? :confused:

Alan

Mike,

for future reference, the fan that sucks air over that sensor in the overhead console is located in the dash. You have to pull out the lining of the glove box and you will see it on your lower right, near the vent. It is a small little thing. With the key in position 2, it should run fairly strong. If this is bad, the climate control will exhibit what you are experiencing. But, I will say, my 420 does the same thing, and my fan is good. I think the thermostats are on the cooler side. I find that putting the dial in the white area, right before the blue, is a nice setting and the fan will eventually drop to medium.

Hope this helps.

Thanks Andy. Today I tried leaving the dial set at the blue/white break (~20*C) and the fan started slowing on the drive home. Looks like everything is correct. I guess I don't need to turn the dial down cold to help cool the car faster in the heat of the day as I was still showing almost 40*F at the center vents.

It did seem kinda strange to be posting an "I'm too cold" post when everyone else it seems is beefing that their A/C isn't cooling at all :eek: :p

Thanks to all.

Mike,

It sounds like you have another big bodied MB on the road. Your posts about this car have started me thinking about possibly getting a big bodied car for a project.

I've gotten things in Europe caught up and don't spend any time there any more. I'm currently working in PA, WV, KY and OH. It looks like I will be working on the West Coast for a while coming up soon. Maybe I'll have a chance to see the newest big V8.

It's kind of a good problem to have when your a/c is freezing you. The climate control is much easier and less expensive to sort out than is an evaporator.

Hope everything is going well.

Have a great day,