It is true that a short circuit will cause the CCU to shut down in self-protection. Whether it will still allow Defrost to work, given that it is the "default" mode, I do not know. Can you find out what brand of CCU you have? There should be a tag on the case -- either Bosch or Kammerer, I think.

You haven't said specifically whether the blower works. Does it? Defrost should cause the blower to run at maximum speed. Does it? Does the blower work with any of the other buttons pressed?

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Yes, the blower seems to respond well when Hi/Low speeds are selected. Not sure about the Auto button in the middle...

I'll need to take out the CCU tomorrow - I'll report back on the brand and Part# - thx for all your help.

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

I have removed my CCU today, but was surprised to find very little identification markings on the unit... I mean every single little bracket and plug on this car has the MB part number... the CCU unit has hardly any - see the pics below.

One emblem I think reads "MK", the short number on the back reads: "8 4586".

Can someone identify the part number for it?!

Attached Thumbnails

     

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Could this be an after-market unit (non-factory)?!

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

The part number is: 126 830 05 85

Be a bit careful with the replacement unit. The earlier 126 830 02 85 won't work with the SDL.

Found this one on eBay:
http://cgi.ebay.com/ebaymotors/MERCEDES-560-420SEL-300SDL-HEATER-CONTROL-126830058588-_W0QQcmdZViewItemQQhashZitem4146165e90QQitemZ280348745360QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccesso ries

It says that it fits 300SDL... but it has two extra digits at the end... will it work?! Has 14 days money back.

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

The seller is some sort of moron, as usual, but the unit is exactly what you're looking for and the price is excellent.

Thx for the quick reply!

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

I purchased a ProGrama rebuilt unit, Go to their website, Google Programa and put in all the info on your car. It will give you part number 126 830 05 85.
They also have a fantastic PDF file with troubleshooting instructions that you can use with your digital VOM. It will actually lead you to the monovalve or the aux water pump or the CCU. I believe I paid around $300 for it with a 3 year warranty.
Print out the PDF file for future use.

__________________
John
1986 300sdl
1985 380se

I downloaded/printed the PDF instruction file - it's a good one. Here is the results so far:

1) Turn ignition off (Ignition Off and my battery is disconnected) - OK

2) Left pin 13 to pin 9 (should be 11-19 ohms); mine had 14.4 ohms - OK

3) Left pin 13 to pin 10 (should be greater than 5 ohms); mine was 7.6 ohms - OK

4) Insure Aux Pump is not seized - How do I ensure that?! Do I have to dig under there and hook up 12V to it directly?!

5) BTW. Where is the cabin temperature sensor on my 300SDL - can't make out the location indicated by the FSM.

What is the function of the Aux Pump anyway... thought the Water Pump moved the fluid around the engine block.

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Cabin temp sensor is located in the overhead light assembly.

The Aux pump purpose is to assist coolant circulation through the heater core when engine speed and therefor engine driven water pump flow is diminished.

Thanks Billybob - found it. Looks pretty dusty up there... Do I need to remove that whole entire plastic cover from the light assembly to get to the sensor? The FSM procedure is pretty 'fuzzy'... and pics in it don't match what I have.

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__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

Take the entire light assembly out and unplug it. They come out very easily. You will then see the sensor and associated wiring and the rubber hose that runs to your aspirator motor that sits on top of the heater duct that runs to your passenger front door. I have found the easiest way to check the aspirator motor is to remove the glovebox liner and look down and to the right.
The wiring plug for the aux water pump sits in a little metal bracket right next to the monovalve . Unplug it and run 12 volts to it and see if it runs.
The Programa website is very helpful!

__________________
John
1986 300sdl
1985 380se

Thank you John; and yes those instructions on the Programa website are indeed very helpful.

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

I just went out to the car to test out the Aux water pump - I unplugged what I THINK is the aux pump plug - can someone verify that that's the proper plug? I measured resistance across it - it measured abou 5.5 - 6.5 Ohms.

When I put 12V across the two prongs I got nothing... I got nothing when I reversed the polarity. If this is the right plug then I think my Aux pump is dead.

Strange that there is continuity in the wire (non-zero resistance) but the pump refuses to operate...

Looks like I have a seized Aux pump... any other thoughts before I undergo the medieval Teutonic torture of pump replacement between the firewalls?!

Attached Thumbnails

 

__________________
1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K