If your blower is not functioning at all, I would advise removing it and applying battery voltage directly to the connector and see if it runs (if you have a single pin connector, then the ground for the power is through the blower motor housing).

If you are having trouble getting the climate control system to produce air flow at the desired location (vent/floor/defrost), that would likely be a vacuum leak. -either in the main vacuum line from the engine to the climate control system, a vaccum valve in the dashboard control unit, or a vacuum leak in one of the hoses going to the vacuum motor/shutters that direct the airflow.

In the rare/extreme chance that you have an ECC system (Electronic Climate Control, typically installed in '88+ 760 & 780), you'll need to pull the trouble codes from the climate control system before proceeding. Post back if you do have the ECC and either myself or someone else will post how to put the ECC into diagnostic mode. The ECC system is identified by 3 rotary knobs on the climate control interface: Blower speed, Air Flow Position, and Desired Temperature (in either degrees or farenheit).

FYI, the climate control system is designed to provide some small amount of air flow when the car is at speed, -even with the blower off. The air comes in through the grill just in front of your windshield, and is forced through the car by the pressure differences between the front of the car and the back of the car as it pushes through the air while driving.

God bless,
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, 258k miles.
'88 Black 780, PRV-6, 148k miles.