Chrysler Repair: 1990 Chrysler New Yorker Heater Panel Vent Controls, air distribution system, chrysler new yorker

Question
Hello,
The a/c and heater works fine and air blows out the floor and defroster, but not the Panel vent that is chest level on the dash.
Is there a relay somewhere that might be out?
Or any other suggestion of what to check for would be appreciated.
Thanks in advance.

Answer
Hi Robert,
The air distribution system is powered by the vacuum created at the intake manifold of the engine. There is a thin plastic vacuum line that branches off the fat vacuum hose that runs between the engine and the brake power booster canister at the firewall just in front of the driver position. So look for that line and examine its attachment to the nipple and also check for a crack in the line. It is routed to the firewall at the midline of the car, directly in front of the heater/ac distribution area. If you don't find a problem with the line in the engine compartment then you will need to find it under the dash on the cabin side of the firewall, right of center, and see if it is cracked or disconnected from the air distribution control. There is also a small check valve in the line on the cabin side which could be stuck in the closed position.
Somewhere along this vacuum line you will find the cause of the problem.
Roland