Climate Control Problems
 

Okay, so I ordered a new climate control unit off of eBay and installed it into my 1985 300sd. The original did not work at all. The new one I put in is not working at all now either. Is there another part that could be causing the problem? Like a relay or something I missed. All the fuses have been replaced.

All the dash lights work and the idiot lights work as well as tach, speedo, and other guages.

Specifics.. Nothing happens at all ? Do you hear the compressor engage when you select a/c ?

Nothing at all. Everything is plugged in but its like it is not getting power or something.

With the system and car on, disconnect the plug on the right side of the control unit and plug it back in. Do you hear any switching behind the dash ?

Okay, here is the new info...

My original MBZ unit has 12 pin connectors, upon closer inspection of this non-oem-MBZ unit reaveals that it has 14 pin connectors. Now what?

I have a spare one in the garage, let me check
 

In the meantime check your old unit for the serial number and compare it to the new one. In my expereince the CCU doesnt fail Catastrophically, it just fails by failing to modulate heat and cold air, butthe pushbuttons work. You must have a break in the harness. Check the schematic and make sure you are getting 12VDC at the power supply connection. Also make sure your vacuum supply to the CCU does not have a leak

The assembly is getting power. All the bulbs and fiberoptics are lighting up. I think the original unit is fried. Can I use the new 14pin unit without damaging it or the wiring on the car.

Where can i find the vacuum supply to the CCU. I don't have a book for this vehicle. I have a 123 manual so I have just been winging it or finding info on this site. The wHunter DIY thread was useful but I am having trouble diagnosing the real problem. I don't think I need to pop the casing open or do any soldering, at least I hope not.

Thanks

The vacuum supply is shown in the vacuum diagrams
 

The vacuum supply is shown in the vacuum diagrams. Basically three lines pass through your firewall off a rubber three way tee. One of these three, the yellow, usually has a check valve on it.

Yellow for door locks
Green for Climate Control
Brown for engine shutoff

If you see any black vacuum lines in the area disregard them and dont touch them.

Put a vacuum pump on the green line and see if it holds vacuum. Do you door locks work with vacuum function.
Do you have an electrical diagram/schematic.
Do a search on this Forum under "Klima"

I haven't checked my extra CCU I will get back to you tomorrow. Let me get my Shop CD and look through it. P dont plug your new one in yet.

Please provide the part numbers for the old unit and the new unit.

It does not appear that you have the correct unit.

There is no vacuum supply to the CCU. All connections to the CCU are via the two large plugs. The vaccum supply goes to the set of vacuum switchover valves that are nestled next to the CCU and radio on the right side. You'll need to remove the right side carpeting from the transmission tunnel to access them, if necessary.

Original Unit- 126 830 02 85 - 12 pins oneach connector

New Unit- 126 830 0585 - 14 pins on each connector

Yep, that's what I figured.

The new unit is from the later W126. It fits the SDL's.

The original unit with the part number indicated is correct for the older W126.

I don't believe that they can be interchanged and have never attempted it.

I fixed my unit...
 

Pull the old CCU apart carefully. check the solder connections between the main board and the two vertical boards the connectors plug into. the joints are soldered and over time the joints crack. It took me a couple hours to fix the unit and now it is working correctly.

My worst fears are now confirmed. The top board is fried. It has three burned out areas. I don't think this one can be resoldered.

Anyway, I have a 300sdl climate control unit with wood and top switches in place for sale. I need to get at least $95 for it. The wood is in good condition and both plastic legs are still attached.

Wish you were offering it about a month ago. I put my third "pre-owned" unit in the '87 with no success.

Finally broke down and bought the Programa unit. Appears to work properly..........but, the low pressure switch is open.:o

Check that the recirculating pump is not seized before you put in a new climate control unit. High amperage from a frozen pump will use the circuit board as a "fuse".

See posts #2 and #3: http://www.peachparts.com/shopforum/general-information/38739-i-rebuilt-my-auxiliary-water-pump.html?highlight=recirculating+pump+fuse