ccu help: heat out the defrost only no fan - PeachParts Mercedes-Benz Forum

uplandbob · #1 03-22-2009, 04:14 AM

Climate control was dead for a year. I cleaned the engine compartment with compressed air and the next time I started the car everything came to life after I heard some clicking noises by the ccu. It woked off and on for a short period then nothing. Pulled the ccu out and hit the push button pins with the solder gun and it worked a couple of times then nothing again!
So California is getting warmer and I'm not going another summer with hot air comming out all the time.. HELP!!!!
1991 300E 2.6 266,000 miles

uplandbob · #2 03-22-2009, 08:09 PM

If ccu is bad why would it start up afer being dead?

cliffmac · #3 03-22-2009, 09:48 PM

then that is not it then? I'd bet that your blower motor is dead...just won't fire any longer...makes the Climate Control seem to not work.....

tinypanzer · #4 03-23-2009, 06:24 PM

Check the strip fuse. It's a 30 amp fuse. I know in a 126 it is mounted near the main fusebox, but not in it. In that case, it is in a separate little rectangular holder.

The fuse is just a little strip of metal, and as it wears out it can become intermittent only working when the two pieces decide to touch.

When you hit the engine compartment with air, you nudged the fuse just enough to make the two withered ends touch. But, because they are so burned out, no real current can pass and your CCU goes nuts with the clicking, etc. until the rest of the fuse burns up. I will be very surprised if you don't report back that this was exactly the case.

I was able to get one for $5 at the VW dealership (MB didn't have it).

Symptoms are a completely dead CCU, no blower.

uplandbob · #5 03-23-2009, 06:57 PM

Tried blowing some more air around the engine compartment and nothing happened. Made a few quick trips around town and it started working a block from the house and it stopped working a half a block from the house.
The fuse looks good! Does that fuse only work the blower motor? Because everthing else works!!

tinypanzer · #6 03-23-2009, 07:09 PM

I think that fuse only does the blower motor, but I'm not sure.

You sure you are looking at the right fuse? Thin strip of metal screwed down on both ends, in a separate mini holder?

The thin portion in the middle gets whitish grey and brittle. If it is discolored, it is probably BAD.

Either way, it sounds as if you've got an intermittent open circuit somewhere. I don't buy the blower motor being bad because it is starting and stopping too often. When the motor starts acting up, it can be a pain to get it to start spinning but once it does it typically runs fine until you turn it off. Usually it's the bearings drying out.

Loose connection somewhere.......