I’ve got a big-ol B3500 van, 1994, with the 5.9 litre engine and 4-speed. It’s got >333k miles on it and it also has the passenger package (High-top) with a wheelchair lift on the rear.

I’m writing because I’m having heater/vent troubles. My specific concern is that I’m not getting much flow from my fan (which I recently had replaced). It's spinning but barely pushing anything. I really don’t get anything from the defrost vents either (as has been discussed -caused by the faulty vac line). I can barrel down the interstate at 60+ and the wind will push warm air into the cabin through the upper vents, though.

When I select anything other than “off”, I’ll hear the fan start then I immediately hear a sound w/in the dash that sounds like a flap closing. This flap seems to be restricting the airflow. I tried to get into the plenum without taking the dash apart but I wasn’t successful.

I’ve read through a lot of material here and it’s been helpful. I found the vacuum chamber behind the R headlight and traced the vac line to the intake manifold. The hose looks OK, but I will replace it while I’m in there. Do you guys still think it’s this vac line or have you heard of this “flap” closing within the dash caused by something else?

 

You need to first verify if the blower is actually spinning or not. That noise could just be the blower conking out.

 

Hi alloro, thanks for the reply.

It's definitely blowing but it's struggling. In fact, for the split-second before the "flap" closes I can feel it blowing fairly well.

I fired it up last night to confirm if it was blowing better from the defrost vents than any of the others but it's not any different. With that info, I'm hesitant to chase the vac issue as THE issue. I still think its a clog in the plenum.

I'm assuming that if I pull the upper dash off, I'll be able to access the ducting. I may start that tonight before the cold spell settles in.