'84 300SD W126 - A/C Question - the saga continues - PeachParts Mercedes-Benz Forum

bodyart27 · #1 06-21-2003, 11:04 PM

So, I finally pulled the stereo, checked to see if the connnections were snug on the back of the thermostat wheel and the Climate Control buttons in the center - still no difference. Basically my A/C is operating like a house system - it cools down to the desired / dialed in temperature, then cuts off completely. The temperature rises and then it will cut on. It will not continuously blow... HELP!!!

Here was the original post:

"When I dial in the temp between 18*- 20* C and just leave it alone in "Auto" using the normal A/C button (one white arrow), the A/C kicks in fine, will vary the blower speed as needed to cool the cabin, side and center vents blow, then "click" - it shuts down 100%. When I mean 100% you can not get the high or low fan to turn on at all. Just still dead air in the car until the temp rises again, and you hear the "click," and the A/C slowly kicks in again, varies the fan speed as needed, then “click” – it’s off 100% again.

Now while it is on its cool down cycle and the A/C is blowing you CAN cycle the high / auto / low, but once it cools off - "click" - dead still air - the fan speed buttons will not respond. It does not matter if I hit / cycle the "O" off button and then the normal A/C button or any combination of the fan buttons (high/auto/off). No A/C or fan until the temp rises in the cabin past where I have it dialed in on the wheel. While cycling between normal A/C and Off I think I can still hear the compressor engage, just nothing blows.

I did try the following. If I left the fan on high during the cool down cycle, it would cool down on high fan speed, cut off, dead air (temp rises in car), then the A/C would "click" and recover on the "high" setting."

bodyart27 · #2 06-23-2003, 09:12 AM

Do I have everyone stumped?

I'm not sure where even to start - replace the CCU (selector buttons in the center between the thermostat wheel and the fan).

I swapped out all the fuses this weekend just to see if that would make a difference - nope.

bueller, anyone, bueller???

leathermang · #3 06-23-2003, 10:16 AM

Ok,,, have you read your 'operators' manual.. to be sure this is not the way it is supposed to work in " some' mode ? Like ' econo' or something.... ?
Did it used to act differently ? Any possibility some 'hidden' switch was toggled ?

Rick Miley · #4 06-23-2003, 10:23 AM

That's definitely not the way it is supposed to run, and it sounds like pushbutton control problem to me. But that's a mighty expensive part to replace without being 100% sure. Try posting this in Tech Help to get an answer from a pro tech.

bodyart27 · #5 06-23-2003, 10:34 AM

I'm pretty familiar with the car as it has been in our family since new. I asked my mom about it (it was her car for 19 years) and she said it would always have the fan on to some degree / speed while in the normal A/C mode (definately not economy as it cools great).

For grins I called my parts guy and they are quoting over $200 for a rebulit unit (he thinks it comes with the thermostat wheel as well and I have to send back the core). I would really hate to make a $200+ "guess" and not solve the problem. Granted that the A/C is working - does this make sense?!

As people have stated before about these A/C systems - went they work, it works great, but it is complicated as hell...

leathermang · #6 06-23-2003, 10:40 AM

Have you looked at the Air conditioning and Climate Control FSM for your car ? The one for the 123 diagnosing procedure is amazingly complicated........ I would not even attempt to mess with...

rickg · #7 06-23-2003, 10:40 AM

All I can offer is an agreement with how you say it SHOULD work. Hope you find an answer. Let us know if you do.

leathermang · #8 06-23-2003, 10:43 AM

Rick and Rick, Yall could save him a lot of grief if you would just tell him that is how it is supposed to work,,,, afterall, he is not getting hot... he just can't here the fan working all the time...

bodyart27 · #9 06-23-2003, 11:15 AM

Well it does get uncomfortable if the Texas sun is baking your side of the car!

I posted to the tech section to see what happens...

Rick Miley · #10 06-23-2003, 11:40 AM

Go to Poop Boys, get a 12V oscillating fan, and mount it on the dashboard. That should take care of it.

leathermang · #11 06-23-2003, 11:47 AM

Sorry, Bodyart... had forgotten you are down here....While RickM's fan suggestion was probably in jest... it would not be out of the question for the time between now and when you figure this thing out....

Rick Miley · #12 06-23-2003, 01:04 PM

I thought everybody in Texas already had those fans.

Oh well, at least all this traffic is keeping your thread at the "top of the heap." Maybe somebody who can actually help will see it now.

rickg · #13 06-23-2003, 01:17 PM

I just meant he was right with this:
"....and she said it would always have the fan on to some degree / speed while in the normal A/C mode ."
The fan shouldn't ever turn all the way off. It'll just kick down to either low of medium once the cabin has cooled down.

bodyart27 · #14 06-23-2003, 05:32 PM

It should vary the fan speed as needed to maintain the temp.

I'm thinking swap the CCU is with a rebuilt unit unless someone has a "but wait, check this first!" idea.

Looking through a search on "CCU" - this is the closest match I could find to my problem:

http://www.peachparts.com/shopforum/showthread.php?threadid=35895&highlight=CCU

--->"clicking" noises. Only happened during cooling cycle, and only when the temp got to the point of regulation, when the CCU switches on/off to regulate temp in cabin." <--- that is pretty much it, but the clicking wasn't effected by driving (rough roads)

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