my heater is stuck on vent, I hear something flapping but get no air to my defrost or bottom heat. I searched the threads but have not found any thing. Is there a cable or a door stuck open. One vacuum hose looked like it had a crack and I fixed that. I have great heat but no defrost or floor heat. thank you in advance.

my heater is stuck on vent, I hear something flapping but get no air to my defrost or bottom heat. I searched the threads but have not found any thing. Is there a cable or a door stuck open. One vacuum hose looked like it had a crack and I fixed that. I have great heat but no defrost or floor heat. thank you in advance.

Currently have the heater on my 86 partially disassembled as I too was getting very little air to defrost, when I flipped the switch I could hear a flap move but got minimal output at the vent. I noticed the vacuum line you describe and mine controls both a vent opening in the kick panel and a controller on the back side of the heater box. After pulling the glovebox for access and the front cover off the heater casing I could look inside and watch the system toggle over for temp control, found a connector to the air director flap has a little plastic connector to the actuator arm that was broken so the door could not move its full travel. The other thing I discovered is that when the truck was assembled there was a weatherstriping type foam gasket put in place at the ductwork connections. When I looked at the duct going up to the defrost there is a 1/2" gap between the duct and the heater housing, it appears there may once have been a gasket in that gap (as the duct is still bolted to the housing) that has long since gone south so I have a nice heated dash but not much defrost. My plan is to jb weld the plastic conector back together and reinforce it with a small strip of aluminum that I can screw to the director flap leaving the pivot point in the middle of the plastic fitting in the proper location and not bound up, then I will investigate replacing the seals with some camper shell weatherstriping and see what I get. Hope this helps.

Thanks for the response. I took the whole dashboard off the rig. Not as difficult as I thought. I found another vacuum line that was disconnected over on the passenger side wall that went to a vacuum pump like the one above the hump in the middle. the door was stuck open which you talk about and the threaded wire was off. the door unit has a tab with a 1/4" screw that when I took it off gave me access to set the door in place again. I am now getting great heat but still have not gotten the flow to the defroster at a high output. One of these days when I change out the factory speakers I am going to look at what you observed. I had a rumble in my car at 60-70 mph, was told it was the range fork in Transfer case. after tightening all the screws and fixing some duct work the vibration is gone. Hopefully that is all I needed to do. Its amazing after 267K that anything still works. FYI, the new engine I just got done putting in runs like a champ.