Volvo Repair: fan, vacuum motors, vacuum motor

Question
I have a 91 940SE.  When I moderately accelerate, the Heater-A/C blower fan will stop blowing.  What could be the problem and how would I fix it?  Thanks!!!

Answer
Serenity,
I don't think the fan stops, but rather you have a weak vacuum at one or more of the vacuum motors that operate the flapper doors that diverts the air flow in the heater/AC duct to the various outlets. It may be a simple as a cracked vacuum hose. The vacuum motors are attached to the duct, and I don't know specifically about the 940SE, but you can usually see them just below the dash. They are about 2 inches in diameter, kind of pancake-shaped, with a small rubber vacuum hose connected to the center. You can figure out which one is causing the problem by removing the hoses, one at a time while the engine is idling, and the heater controls set in the position where you are having problems. When removal of the hose causes loss of airflow at that same outlet, that is your problem vacuum circuit. Then you can trace the hose back to the engine to see if you can find any cracks.Of course, it could be the vacuum motor itself, although they don't go bad too often. I hope this helps.