Hot Da#n... Summer in the City

[JPL]

Really a question about troubleshooting Climate Control on a 79 123...
With Servo - style ACC

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. Please let me know if you need more information.

I have done a few searches and found some excellent suggestions, but I thought....'while I have the center console off, I may as well look at everything." Waddya think?

Thanks,
James

[JPL]

No nibbles yet on this tasty bait?

I know its long winded, but any suggestions would help.

Thanks,
J

I have the same exact problem as you describe with low flow at the center vents on both my 1980 300D and my newly acquired 1983 300SD. Did you ever get this resolved?
Robert