I think my 93 940 has some kind of vacumm leak which controls the ventilation. With fan on at #1 or #2 setting, the flow is weak. As I drive a steady mph, the flow gets stronger. I think it is some kind of vacum leak. I am not sure where to check for a cracked hose. Is there one in the back of the ventilation control on the front panel? If so, how do I remove it. and if someone has a vqcum diagram for the ventilation system, it would help. Thanks

 

the vacuum line starts in the engine compartment and it has a disc shaped one-way valve in it before it goes through teh firewall, not far from where the heater hoses go through. some 940's have a vacuum bottle (plastic thing that looks kinda like an egg crate) behind the dash, (although that may be mainly on turbos).

this vacuum line goes to the back of the HVAC control panel, then there's spagetti tubes from that panel to each fo the vent actuators on the airbox, and another to the heater valve thats between the engine and the firewall.

 

Seems more like an electrical issue to me. The vacuum system opens and closes vents and doors, but I don't think that would effect fan output.

Do your headlights dim at idle and brighten as rpm's increase?

I am, however, ignorant of your car's climate control.

 

on a 740/940 with the manual climate controls, the fan switch has 4-5 positions, each is a wire to the resistor block on the side of the fan enclosure, behind/below the glovebox. that resistor block certainly can get baked and stop working reliably.

 

I may have mislead you folks on my ventilation problems. I replaced the fan a few years back & it is running great. Pierce is on the right track in that I think I have vacum problems. The hoses back there I think are original. I think it is in the control that directs the flow to upper vents etc. Not the temp control--it is fine. Is it hard to remove the panel to get to the vacuum control to examine the vacum control **** assembly & hoses? Thanks.