PeachParts Mercedes-Benz Forum - View Single Post

JPL · #3 06-13-2002, 08:13 AM

MVK:

I have an alert ear to the advice you are giving Russo. I am experiencing the same issues in my 79 300 CD (123 - with "servo' styled climate control (MB Manual - ACC II).

Your troubleshooting steps give me excellent incentive to takle this issue myself. I have a mityvac, and will begin my testing.

My question is do you think I should start with the vaccum elements just behind the ACC, or should I look at the ones that are under the dash first? I think, upon looking at my MB repair CD manual, the ones under the dash are called"flap" elements. One for the legroom flap-lever, one for Defroster Nozzle Flap, and ( this one is a b*tch ~ Center vent flap. Luckily, I get air out of my center vents, but just a little cause its all going out the defroster vents.

First I will describe the symptom:

My symptom is that most air flows through the defroster vents during all stages of the climate control. This happens with the compressor switch on or off, temp dial set to lower temperatures and higher temperatures. Some air flows through side vents, very little air flows through center vents, no air flows from leg vents. The temperature of air flowing through these vents changes in response to temperature dial settings and / or compressor switch changes, but the vents do not open or close in response to changes in ACC button selections. The fan / blower speed responds correctly to button selection changes, as does the force of the air, but, as stated earlier, most air flows through defroster vents, with only very little (leaked / incidental) air flowing through side and center vents.

Additionally, at someone’s suggestion I tried the following:
1. Without starting the car, but activating the ignition, choosing the DEF button resulted in airflow (through defroster vents), choosing Auto-high, no airflow.
2. Start Car. Press Auto-Hi, blower starts once auto reaches temp (about 45-60 seconds)
3. Turn off ACC, Switch off ignition. Wait 10 minutes, turn key to just before starting, select Auto-Hi. Airflow immediately

I believe this test was to confirm that there is not a vacuum leak coming into the ACC system, and that perhaps my troubles are with a leak within the ACC system. Also service records from the PO show that the servo, amp and center dash vent actuator were replaced in June of 1999 along with a Freon recharge.

So, after all that, here are my questions:
1. Do you think that I should start with changing the Vacuum Changeover Valves? (FastLane # 14045-12000, or 04045-70190, I am curious about the differences between these two.)
2. Should I change other vacuum elements:
a. Defroster Nozzle Flap 04010-25703
b. Legroom Flap Lever 04010-25709
c. Defroster 04010-25709
d. Legroom Flap VE 04010-73599
e. Center Vent Circulating Flap 04010-56034

Have you seen this symptom in the past? What do you recommend? I hope that I am not asking too much, but hope that you can offer a bit of guidance.

Thanks,
James