Vent doesn\'t work OK, I give up, I have tried and failed to determine why the Bi-Level and Vent positions of the controler on my 1973 Blazer don't seem to do anything. All other positions funtion corectly, the vacume motors are good and I'm getting good vacume signal to the valve. I have checked the valve in and out of the vehicle and even verified the same problem on other similar year vehicles. The valve just doesn't pass vacume to the vent motor when in the vent position. Is this a factory defect or what?