w126 Climate Control Issue 300 SDL - PeachParts Mercedes-Benz Forum

cgryphon · #1 03-13-2011, 01:34 PM

Last month my climate control started running on low fan all the time the car was on (anytime the key was in position 2 or running). Can't shut it off no matter the switch position, etc.

I tried resoldering connections, but still the same.

I got a junkyard CCU, still the same.

Exact same symptoms, which I thought was strange. Low speed all the tme, even when switched to the O button. Auto and high speed work with both CCU's.

While replacing the CCU I decided to try the key on, with everything disconnected. The whole panel and all switch connections removed.

CRAP, the fan is still running on low speed. I was expecting that nothing would run without these connections made.

I also note that when connected, I can hear a "click" somewhere inside the dash (not the CCU as I was holding that in my hand) when I try to switch the fan off using the O button.

What's the clicking noise? It's like it wants to switch off but no joy, just clicking with every push of the O button. Same issue with both CCU's so I'm thinking it is something else.

Any ideas?

Thanks,

Clay

cgryphon · #2 03-14-2011, 03:30 PM

ttt for a possible answer?

SD Blue · #3 03-14-2011, 09:28 PM

Hmmm......not sure if yours is the same but doesn't it have a blower speed controller?

ah-kay · #4 03-15-2011, 01:29 AM

I look at the schematic on the Aux fan. There are 2 relays controlling the aux fan, K9 and K10. K10 is pre-resister ( R15 ) which controls the slow speed. K9 is after the resister for high speed.

If K10 is faulty then the aux fan will be running all the time. Your K9 is OK as high speed is working. High speed by-pass the resister R15. I think K9 and 10 is inside the fuse box at the back. The ice cubes. Pull them and see what happens.

Good luck.

ftwchopper · #5 03-15-2011, 08:03 AM

When my blower motor was stuck on high in my 123,it turned out to be a faulty blower control relay located behind the glove box.
No matter what button i pushed on the ccu,the blower motor remained on high.It eventually got the fuse hot and burt it out......

cgryphon · #6 03-15-2011, 12:05 PM

Excellent info on some things to try!

I will investigate the K9 and K10 relays to see what happens.

Also, I will go behind the glove box and see what is there.

Driving home from work yesterday I noted that with the CCU "O" button depressed, and the low fan button depressed, I could hear an occasional clicking from somewhere in the middle dash. I wish my hearing was 20 years younger!

Thanks to all for the replys. BFOTN (Best Forum On The Net)

Clay

cgryphon · #7 03-16-2011, 09:42 PM

Cube relays in the fuse box are labeled C,D,F,H,I. Did not see a K9 or K10. Put the key in position 2 and the fan started running as usual. CCU with depressed "O" button and fan on low speed.

Removed all the cubes, one by one, no change, fan still running on low.

Took out the glove box liner to look for a relay somewhere in there but could not find one.

When I press the "O" button I can here a click. I think it is coming from somewhere just right of (facing forward) the CCU. Said another way, just left of and slightly below the glove box.

Going to remove the passenger kick panel tomorrow for a look under there.

ARRRG

Clay

ah-kay · #8 03-16-2011, 11:39 PM

If you unplugged all the cubes in the fuse box and the aux fan is still turning then it is possible you have a short somewhere. K9 and K10 should be in there. Do a search on K9 and K10 and there should be a lot of info related to Aux fan. K9 and 10 are what is on the schematic and it may be labeled differently in the fuse box.

There is a resister ( R15 ) under the brake reservoir, difficult to see but it there. Check whether you have 12V on the terminals. If there is then you need to find out where the 12V is coming from. That is what drive the slow speed.

Good luck.