I have a 1990 740GL that has no air flow from the heater/ac vents. It does not matter what setting I set the sliders for, no air comes out. Hot or cold, Defrost or floor or face. Not even enough to move a tissue.
The blower motor was making a ton of noise on speed 4, so I replaced it, hoping that was the issue. No luck! It is however now allot quieter.
On the passengers side of the heater box is a little panel that can be removed, that appears to hold some sort of pre-heater. With this panel off, the blower will push enough air out this hole to rustle a newspaper in the back seat.
I can hear the vacuum hiss while moving the control levers, and the vacuum supply going through the firewall is strong on the engine side. I can also watch the 'actuator' on the upper passengers side of the heater box move when the heater selector lever is moved from floor to defrost.
Any pointers?
Charlie