heater not blowing correctly (vacuum related)
 

I have a 91 B-250 and the heater doesnt blow like it should. I replaced the blower motor from napa a while back, and the electrical has been tested and cleared. It just down blow enough air. I think there might be a vacuum diverter in the dash that isnt working correctly. Sometimes, if I stomp on the gas, the air will stop moving until I let off. Also, sometimes when Im on the freeway, it seems to blow great. I have no idea how to get into the dash and check out the air ducts. I cant find any instructions anywhere.

Could it possibly be the heater switch assembly? Could I have gotten a bad blower from Napa? Older dodge vans I
ve had, had kick ass blower fans. They usually kicked TOO much ass, as the positive to the heater would get too hot for the fuse box.

Anyone experienced this?

I delt with the same issue. Under the a/c dryer on the passenger side of my van. There were two vacuum lines attached to a vacuum motor. The motor had a bad seal. So I replaced that with the two vacuum lines and my a/c has been blowing bad ass ever since. I'm not sure it would be the same issue with you but it's more than likely than under the dash. This vacuum motor controls the door for max or norm. Yours might be stuck in the middle. Good luck

Thanks Russel. I took a look and saw what I think you're talking about. Kinda looked like an automatic choke but bigger, had two vacuum lines and a rod going towards the dash. I hope its not as much of a pain to get too as it looks like though.

Sounds similar to the problem I'm having with my a/c fan. Same symptoms, when the vacuum is low, like in high engine power demand situations, a/c fan air seems to disappear altogether, and as vacuum increases doors open and close and the air finally starts to come out of the dash. Even on high the air output is nothing to write home about. My understanding is there is a small check valve in the dash, behind the radio that sometimes goes bad. (I can see it with the glove box out.) I also think I have a couple of small vacuum leaks under the hood on the fire wall that isn't helping either. The vacuum hoses are small, old and dry. I'm going to start replacing them one at a time, that and replace that small check valve too and see if it doesn't solve those issues. Not sure if this will help your situation.

RH, I had to loosen the clamp around the a/c drier, the round little tank and lift it up some to get my hand under there to the vacuum motor nuts. The rod has a vertical then horizontal bend at the end. It sits in the hole of the door mover tab.

Yesterday, I turned the van on , and had my roomate sit in it while I took a long pair of needlenose pliers, and manually pulled the rod in and out, and it made no difference at all, unfortunately. I could also tell that the rod was sucking in the motor by looking at the end of it. I wonder if its possible that it disconnected from the door mover.

I have to update this. After YEARS, I finally figured it out. I took the whole heater box assembly apart twice, looking for some kind of door that wasnt working right. I've tested the electrical, even had a mechanic look at it. Long story short, The fan must have been designed for vehicles with the heater on the other side, so it was blowing backwards the whole time. I switched the wires around, and voila. Feel a little like a moron, but I did finally get it. It never dawned on me that the fan might be spining the wrong way. On a hunch I discinnected the wires, turned teh van on, and connected them, so I saw it go backwards.....

No there are no reverse designed systems. What happened is some guy got back from his liquid lunch and stuck the wires into the connector backwards.