Volvo: 940 blower acts odd, vacuum motors, vacuum system

Question
Hi Ray,

About that 940 I said just a few weeks ago was running so well? Ha! It has a new issue: Air conditioner hasn't worked for a year or more, and I tried to have it fixed, to no avail. So, here in the north, I can live without. However, I do like the blower. But now it only seems to blow when I am not accelorating. The defrost seems to work fine, but the blower blowing cool air into the car and my face only works when I lift off the gas. What to do? Is this one of those famed electrical issues of 940s that I hear about now and again?

Answer
Lynda,
So the blower motor continues to run and the vents shut down on acceleration. You are losing vacuum to the vacuum operated motors that open the vent doors. There is either a check valve in the vacuum system that is "leaking back" or one of the vacuum motors itself is leaking. One of the most common ones that I see leak is the double diaphram one on the left side, under the dash. Make sure that the check valves in the engine area are good before going under the dash. You need to have the system tested for leakage and correct that leak for the vents to operate during acceleration.