Quick ACC Question

[JPL]

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