W123 climate control only rarely works at all - PeachParts Mercedes-Benz Forum

Maroon 300D · #1 01-08-2006, 09:49 PM

Hi!

I bought an 85 300D Turbo two days ago and I am already having some problems that didn't exist when I drove the car home. I have been able to solve or at least figure out most of them through previously posted info. but this one is stumping me.

The climate control, which worked well just two days ago, will now hardly work at all. Once in a great while it puts out just a little bit of air for a short time, and today when I turned the key to '2' it was working full-blast for a couple of seconds and then stopped.

I don't know quite what to make of this, so if anyone has ideas they would be appreciated!

Thanks.

kerry · #2 01-08-2006, 10:05 PM

There are two manual speeds for the blower, top and bottom buttons too far right. Center small button between them is auto. Try the manual speeds. Also try far left button--this is defrost and overrides other controls.

Gigtime · #3 01-08-2006, 10:26 PM

Sounds like the climate control unit. I believe there's an article on
how to rebuild it in the DIY section. The 85's ccu is easier to rebuild
than the one on later models. Or you can buy a rebuilt one in the
200 to 225 range.

See what happens when you put it on defrost.

Bill

Maroon 300D · #4 01-08-2006, 11:18 PM

Ahh!

I hope you're wrong, Gigtime. I will try moving the key a little.

It doesn't seem to make a difference whether I have the fan on high, low, or auto. I believe it has actually been on defrost the couple of times it has briefly worked again.

Thanks a lot for helping me out, everyone, and if there's anyone else with ideas I wouldn't mind hearing them.

Maroon 300D · #5 01-08-2006, 11:20 PM

Oh yeah - is there any difinitive test that would prove it's the ccu?

Obviously if the key thing works than it's the ignition switch, I suppose, and I understand that's a relatively easy fix.

Gigtime · #6 01-09-2006, 12:59 AM

Well, you won't like the "definitive test" I've used. I've replaced every
other component of the system and that's the only thing left.

Actually I did need a new compressor and other parts but I replaced the
blower motor and regulator and I now believe I didn't need to because the
CCU is the culprit for my current problem, which btw, is very similar to yours
with the exception of the key thing.

My AC comes and goes on it's own usually at random intervals and it never
stays on longer than a few minutes. The only cause and effect related action
is if I adjust the temperature while it's cooling, it will go off within a second
or two.

I would try the re-soldering technique recommended elsewhere on this site
if I were you. My car's an `88 and that method isn't that effective with my
CCU because you can't get to all the circuit boards in those units. With the
85, you can.

Bill

Maroon 300D · #7 01-09-2006, 04:12 AM

Ok, it sounds like it probably is the ccu.

I think I found the DIY info you were talking about (it's at http://207.210.95.34/~boostd/Climate/) and if that's really all I have to do, it's not as scary as I originally thought. Too bad yours isn't so easy.

I really appreciate the help. Thanks a lot!

Gigtime · #8 01-09-2006, 03:09 PM

That's the thread. Let us know how it turns out.

Bill

meltedpanda · #9 01-09-2006, 03:53 PM

Can you "jump start it" but pushing in the defrost button?
This can help with diagnosis
If it does could be the temp interlock circuit, fan regulator or temp sensor,if not then it could be ig .switch or perhaps the ACC unit itself

Maroon 300D · #10 01-12-2006, 12:59 AM

I have not been able to get it to work in the last few days at all.

The defrost doesn't work. I wish it did because here in the Western Oregon it has rained for the last 30 days or so and it will probably rain for the next 30 as well. I am having to drive with the windows down (the two that work - need to fix the switches) because if I don't I have to wipe the moisture off the inside of the windshield about every two minutes.

I will probably take the CCU out Saturday and attempt to fix it.

meltedpanda · #11 01-12-2006, 10:41 AM

I would lean to the CCC unit , as MB built in that the defrost mode is the fail safe mode, when all fails at least your window should defrost.
With that in mind make sure you are NOT getting power to regulator or fan to ensure that the CCU is the culprit

Maroon 300D · #12 01-17-2006, 01:02 AM

Well, I was going to test the regulator and the blower, but I couldn't immediately locate them so I decided to just take out the CCU and try the soldering technique. I was a little disappointed at first because the solder looked fine, but I decided to go ahead and add a little to the skimpiest areas, and when I popped it back in it actually worked!

It actually appears that the temperature regulator doesn't work but this may have been the condition the car was in when I bought it (I only had it one day before the fan stopped working). I will fix that another day, but for now my defrost works and that's all I really need.

A couple of other things: I found the button assembly very difficult to get off until my fiance figured out that you have to pop the infdividual buttons off first.

Also, I tried turning the key a little in the ignition to get the fan to work at one point and after my experience I would warn you not to try this in traffic on a busy road. The car shut down entirely and I sat there for about 20 seconds. Fortunately everyone just went around me.

Thanks again for all the help, everyone.

meltedpanda · #13 01-17-2006, 11:33 AM

Great, just remember the defrost is the fail safe, if this is working now, other parts may be involved that are outside of the unit itself
As you say ..... another day