Started to tear into why my blower fan works on defrost only today. Removed blower motor housing, brushes looked fine, works with 12volts appliednand when defrost is selected. When pushing buttons for AC on Ccu here clicking noise, aux water pump works. Does this sound like a bad Ccu unit? Is this one that can be rebuilt or resolderd? I see write ups on the board, but this unit looks different. Anything else to check?
Thanks

Forgot to add, could this be an issue with the blower regulator? Where is it located and can you test it?

If fan is blowing on one setting, it should blow on all settings except off. Fan is NOT the issue.

Likely, it's the CCU and/or the vacuum modules. A bad vacuum module would only allow heat to blow via defroster (it's the benign failure mode). Sometimes, the soldering joints on CCU are the culprit. Many folks just do a quick re-soldering job and many things begin working again.

Check your modules and their vacuum supply for faults and inspect your CCU.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

Thanks, I did just have a vacuum issue with the door locks that ended up bypassing so I could turn off. Are the modules for the AC behind the dash? Any write ups on checking that stuff? So vacuum can cause the blower not to work when a/c high or lo is selected.

Yes the vac pods are BURIED in the dash. Are you HEARING the fan when you are not getting airflow? If so, then it is likely a vac pod issue. Do some research on how to check them before going into the dash. If you DO go into the dash, replace them ALL while you're there.

Hope this helps.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

Larry, thanks. The fan will not run unless defrost is selected. I had originally thought this was a brush issue in the blower but they look fine.

Hope this is correct. Considering your conditions try applying ground to the plug for the regulator. If the motor runs with the ground applied then the problem is the regulator. The regulator causes the application of ground to the motor. Without the ground the motor's circuit is incomplete. I did it (if I have all this right) by running a wire from the neg battery terminal to the plug above and behind the brake booster. In my case I replaced both... before I found out there are cheap versions of the regulator available. Replaced just the motor and reused the squirrel cages. $80

Okay, you have the evil servo unit. I am assuming you have your AC charged and it was done with freon? Not 134.....I haven't gotten to the AC part of my ccu yet, but I have been up and down the system. If your servo is working and the aux pump isn't frozen then the other 2 things to replace is the computer behind the glove box liner, they get pretty burnt up....the computer controls the blower motor as well as the servo as well as the push buttons. There is also an air temp sampler tube that is made out of foam...that disintegrates....this runs from a hard plastic tube from the blower motor area to the passenger side speaker grille....you will see the little temp sensor in the grille...you also have a fuse for the entire system that is located on the drivers wider fender well by the relays...oh and the ccu will not come on if the cabin temperature is higher the what the dial says....with out the sampler tube the ccu will not know the cabin temp....also dash dollies will block the sensor....

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Looking for the blower regulator up by the brake master cylinder and cannot locate it. Does anyone have a picture of what it looks like?

You don't have one.....look up evil servo

Read this

http://www.peachparts.com/shopforum/general-information/240606-evil-servo-service-manual.html

Re read my post! Others are posting about post 1981 Mercedes 300D's....

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Thanks cooljjay