Quick ACC Question - PeachParts Mercedes-Benz Forum

JPL · #1 06-05-2002, 09:25 AM

Hello;

Upon searching I could find nothing specific to my question, but lots of great Automatic Climate Control tips.

Anyway, if I step through that quick "early ACC (vertical style control w servo)" test in my 79 300CD, my vent flaps do not respond. For all the steps available (i.e. auto-lo, auto-hi, bi-level, defrost, compressor on or off) the flaps do not respond. The leg flaps remain closed at all times, the center, side and defrost flaps remain open, or partally open, at all times.

Do folks think I should replace the vacuum elements for each flap, or should I be looking at something else? Where is the most likely spot for a vacuum leak? My brakes, trans, locks, trunk, fuel door all seem fine. What else should I look at? I am getting heat when temp dial is turned up, and (last year, I currently need a recharge) I got cool when the compressor was switch on. For heat and cool, all air came mostly through the defroster vents. Just a little through the center vents. None from the leg vents.

Any suggestions would be welcome. I am looking at an article that LarryBible has distributed, but it does not address my very specific airflow checks.

Looking for suggestion,
James

psfred · #2 06-05-2002, 08:40 PM

You don't have vacuum to the climate control. Look for a loose line (the green ones are climate control) in the engine compartment or under the dash. There is a restriction orifice (yellow or white "but connector") in the line or at the connection to the main vacuum line that goes to the brake booster -- these can get clogged, reducing the vacuum to the climate control.

The best way to check is to get a MitiVac hand pump and try pumping the green line down by hand -- if it won't hold vacuum, you have something seriously wrong under the dash, it if does, plug the Mitivac into the other end of the line with the engine running and see what kind of vacuum you get. If you get good vacuum with the hand pump and the flaps still don't work, you have something wrong with the control unit (very rare). At worst, you have a weak vacuum pump that needs work or replacement.

I had the same problem on the 300D recently -- turned out to be the turbo recirc and EGR actuators are leaking badly -- the car still shut off fine, but there wasn't enough vacuum at low speeds for the tranny to shift properly or for the climate control to work. I plugged the lines until I can get replacement acctuators.

Peter

JPL · #3 06-06-2002, 08:04 AM

psfred;

I ordered a mityvac just the other day, so I should get it shortly and will go through the steps you suggested. I kinda figured it has something to do with vacuum, but with so many vent vacuum elements and vacuum switches and check valves, I was a bit puzzled about were to start. Thanks again.

james