Marty I have a 1991 350SDL that has the center vent not

Posted on Feb 7, 2014

A 1991 350SDL that has the center vent not blowing air issue. However, When I get on it and the revs go high, air does move from the defrost vents to the center vents. Does that mean that the actuators are ok and I have a leak somewhere else or does that mean I still need new actuators. Either way, I`ll need your help to track it down and fix it. Not that I know of. I have only had it for about 6 months.

Marty I have a 1991 350SDL that has the center vent not
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Here is what I can tell you. The transmission will sometimes hold a gear instead of upshifting until I lift off the gas. I brought it to a mechanic and he felt the transmission shifted well and it was a vacuum issue. The second thing is that the vacuum valve off of the injection pump has some vacuum tubes that go to a valve near the drivers wheel well. That same valve has some lines that then go into the inside of the car. One of those lines is disconnected and capped. Today my mechanic said I needed to replace 4 valves in the dash in order to be able to get my AC to blow colder. But I do not believe he saw the capped line. I think he just thought that the valves were bad (which they might be). The last thing is that the air does in fact come out of the center vents when I floor the car and the revs go up for a few seconds. After I lift off the gas, the air flow will go back to the defrost vents. I believe I can hear the flaps going back. I really have no way to check for a vacuum leak and having previously seen a vacuum diagram it looked like there must have been hundreds of lines that probably are not easy to get to. Ok, let`s start with a vacuum schematic of the system and the location of the main switchover valve. Step one is to be sure we have adequate vacuum from the vacuum pump going to the switching valve (Y7). You can start by checking it under the hood at the source. Then you`ll need to access the valve alongside...

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