I haven't driven my '88 190E 2.6 special order five-speed for a bit over a week, and today when I started the engine the HVAC fan was on full speed despite the control lever being set on the lowest speed. I fiddled with the HVAC controls, fan control slide, and temperature control wheel, but nothing seemed to work.

I went ahead and ran several errands and continued to work all the HVAC controls, but no change. With several errands the ignition got cycled several times, but no change.

It wasn't until I got home and opened the door before I shut off the engine that I heard the dual aux. electric cooling fans were also on high speed even though the temp gage was at 80C and had not exceeded 85 during the drive. I had not heard them before, perhaps because of all the noise from the HVAC fan.

I'm thinking the so-called KLIMA relay may be the culprit or, perhaps, even a fuse. I'm going to poke around, but would appreciate any advice, especially from someone who has experienced this problem on a similar vintage model.

I'm really perplexed. Is the full-on HVAC fan and aux. electric cooling fans being on high speed connected in some way or is it just coincidence that the two problems happened at the same time?

I may have to start calling it the "Mercurial Benz" again, which is what I called it during the warranty period when it had a lot of problems, but mostly small, and I've kept the car all these years because I've always really liked it.

Duke

I got around to doing a little troubleshooting today and I wanted to at least shut off the aux. electric fans and heater blower motor, so I started with the fuse box. There are several fuses that appear to apply to the aux. electric cooling fans so I went down the list and got the following results pulling fuses.

1 - relay 1 aux. fan/engine fan term. 86... no change

3 - aux. fan... no change

10 - electromagnetic clutch and other functions... no change (This model does not have an electromagnetic fan clutch. It has a viscous fan clutch.)

2 - A/C compressor relay 2 aux. fan term. 86 and other functions. bingo, aux electric fans shut down. I reinstated 1, 3, and 10, and they stayed off.

The fuse box cover states "fuse blower motor outside fuse box". I see a couple of fuses that appear to be on the blower motor circuit on the wiring diagram, but the location isn't indicated.

I removed the cowl screen to see if I could find an electric connector for the blower motor, but it was not obvious. The motor is inside a case and it appears to have a cover that can be removed to expose the squirrel cages and motor, but I decided to research the documents I have before going further.

I'd like to at least get the blower motor shut off. I've got some short errands to run later this week and with the mild SoCal weather I can do without the HVAC system and it has a new engine driven clutch fan installed last year so the aux. electric fans won't be needed. About the only time they ever come on is the biennial loaded tailpipe emission test on the dynamometer.

Any help appreciated...

Duke

Well I never owned a w201 but do know lots about a w124 of the same vintage. Both the aux fans in addition to being controlled by the kilma and the hvac fan are also controlled by the climate control unit ccu. A connector for the hvac fan is on the firewall beside the brake booster, disconnecting that will stop the fan if it exists on the 201. Another ccu maybe required. Hopefully that helps?

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

My '87 190DT is long gone, so I have no car, no books and only my fading memory. Nevertheless, as I recall, the blower speed control is built into the switch, so if that's shorted you're going to have to find a switch. The '87 had an auxilliary fuse box mounted just forward of the main fuse box. This was a black plastic box, and it held a pair of relays and some fuses. I'm not sure if this was present on all models. This is how it looked in my car, the orange relay controlled the high speed fan. The original black relays were internally fused: as they aged, the heat from the fuse could cause the contacts to bridge. The orange relay has an external fuse, and fixed that problem:

Thanks for your replies. I couldn't find what looked like a HVAC fan connector near the brake booster or anywhere near, and my car doesn't appear to have the box as shown in the post #4 photo.

So I decided to remove the fan switch and CCU (with all the pushbuttons and temperature control.) The plastic trim panels surrounding these began cracking a few years ago. I may have made it worse, but I can probably make at least a partial repair with superglue and epoxy. I don't know if replacements are available, but I'll look around.

Once I got the fan switch and CCU out and electrically disconnected I turned on the key and no fans came on. So I switched off the ignition, replaced the #2 fuse and the aux. electric cooling fans remained off, so I should be able to drive the car, at least for short tripos.

The CCU has two ten pin connectors so I attached each one separately and no aux. fan with the ignition switch on, but they came on with both connected, ignition on. With the CCU electrically isolated, connecting the HVAC fan switch had no effect at any position.

I removed the bottom cover from the CCU, which exposed the bottom of the circuit board. It looks brand new.

Since the buttons don't work I figure the CCU is not getting power. I need to study the wiring diagrams I have, and see if I can figure anything out.

Does anyone know if the CCU is reparable?

In the meantime anyone familiar with these 80s-90s HVAC systems, any model, please chime in with any thoughts you might have.

Duke

Duke, Can you isolate the fan switch and use an ohm meter to see if continuity makes/breaks between the pins as the fan speed is changed? If it has continuity on the high speed pins in any other mode the switch would be internally shorted.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Yes, the fan switch is the likely problem.



If George Murphy is still around, he may be able to help with your CCU:



https://www.perfanalysis.com/

Just thought of something: did you try disconnecting the switches on your receiver dryer? As I recall, the A/C will trigger the fans at high speed if the pressure is high. But it may be that the switch is stuck.

Reach out to ProGrama re: CCU repair.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks for the additional ideas. This morning the car started normally with the HVAC switch and CCU removed, and I was able to make a grocery store run before SoCal gets some rain (FINALLY!) over the weekend. (I'm about five miles south of the LAX tower separated by at least 15-20 miles of suburban sprawl from any potential wild-fire source.)

The only glitch was the turn signals didn't work. This happened a year or so ago, but they came back. I tested them during the recent work over the last couple of days, and they did function, but recalled that I first tested the four way flasher, which worked. So I turned on the four-way flash for a couple of seconds then shut it off and tried the turn signals again and Voila! they worked. Oh, the "Mercurial-Benz"!

I've got some outside work to do in preparation for the rain, but I'll get to the recommended tests by at least this weekend and will report back.

Duke