W126 No blower after replacing CCU and blower control - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 09-14-2015, 08:30 PM

1991 350SDL The blower/fan quit working the other day during a hot day, but worked in the morning when the car was cold. I turned off the car to go into a store, and when I came out, the blower did not work again. I pulled the lower panel and checked for power at the blower connections=no power. I powered up the blower, and it works great. I then went to my local wrecking yard and got a blower control from a 126 and installed it. Still no blower function. I then went back and got the CCU thinking that was the problem. Installed the CCU, and still no blower. I took apart the original CCU and re-flowed the solder joints and installed it. Still no blower. I found another CCU in my stash and tried it. You guessed it, no blower. I then tried all combinations of blower controls and CCU's, but still no blower. I checked all the fuses including the one for terminal 86, and all are good. I put everything back together with the replacement blower control and original CCU. The next morning I went to drive the car, and the blower worked great until I shut the car off to go in the store. Again, I came back out to a non-working blower. Is there any other component that would hinder blower function if the CCU and blower control are good? I can't imagine that I have three bad CCU's and two bad blower controls. Any ideas?

pmckechnie · #2 09-15-2015, 09:01 AM

Did you check the external fuse that should be somewhere close to the fuse block. They can look good but have a hair like crack that is not obvious. Check both ends with a meter or test light to a good body ground with the car running and the A/C system on and set to high blower speed. If there is no power there then you may have a bad ignition switch or a bad connection somewhere. If you do have power at the fuse then check at the blower control unit for power. I don't know the pin number but it is the big red wire I believe.

paulm

ROLLGUY · #3 09-15-2015, 10:30 AM

Quote:

Originally Posted by pmckechnie

Did you check the external fuse that should be somewhere close to the fuse block. They can look good but have a hair like crack that is not obvious. Check both ends with a meter or test light to a good body ground with the car running and the A/C system on and set to high blower speed. If there is no power there then you may have a bad ignition switch or a bad connection somewhere. If you do have power at the fuse then check at the blower control unit for power. I don't know the pin number but it is the big red wire I believe.

paulm

The blower works when the car is cold, but does not come on again after the car is turned off. It is hard for me to imagine it would be a fuse if it works sometime, and other times not. Also, on this car it has an actual fuse for the blower in the fuse panel (#5 I think?).