This one is about the CCU. I have AC and heat, but the fan works when it feels like it. I read how to work on the CCU and to check the solder joints and they were all good with no breaks. I cleaned them all. and noticed that on the back of the board two traces had gotten hot or broke somehow, these were on the same side as the temp wheel. and at the back of the board. I resoldered the traces to where the came and went to make a connection. Fairly easy job.
I re assembled the CCU and re installed into the dash, bput the radio back and the ashtray and buttoned it up. I started the car and all was well I rolled the temp wheel to the coldest setting and I heard a motor running slowly in the passenger side under dash. I rolled it the other way to most heat and I still heard the motor running. If I rolled the wheel to the mid setting(26) it quit, if I then pushed any of the buttons it came back on. If I centered all buttons it goes off. What have I done, and what is running. I isn't the fan because there is no air flowing out of any vents.

Every once in a while the fan will come on with the AC running ...or the heater. I think this model has an aux water pump for the heater. Is this what I'm hearing running?

I figure that it is time to replace the CCU?

Is it a W116?

If so, you are hearing the servo motor.

The fan should always run on high in defrost. It may run in Bi-level. It will only run in auto if the engine temp is above 104F and the vacuum hose has not fallen off of the bottom of the servo.

There are two fuses in the fuse box that look like they were added as an after thought. They were. One is for the climate control amp and the other is for the servo?

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

From his name, I'm assuming it's a 1984 380SE. W126.

Check your auxillary water pump re: the burned traces on the CCU.
http://www.peachparts.com/shopforum/showthread.php?t=140870&highlight=auxillary+water+pump

Check fuses (may be an add-on fuse, as described by 250 Coupe.

Check blower motor (smack it); may be brushes/commutator)

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Oops

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

Thanks guys,
Yep it's an '84 380SE Midnight blue with grey interior and 182,000 miles.

I'll check this out today. I'll install a fuse to the Aux pump also. Sounds like good cheap insurance. I was sure that Aux was what I heard running. The fan has a mind of it's own. just comes on at will and runs a few minutes or seconds and goes off. That is why i think the fan motor is fine just electronic to and frm? are messed up. I just went and grabbed some coffee and though not really cold here this morning, the heater on low did heat the cabin(front anyway ) without the fan. I'll get this old girl sorted out. I think she likes being driven after her "vacation". I think I'll look for a rebuilt or good used CCU unit as I don't trust this one now. However all the solder connections are fine, not cracked, just the two traces were fried.