Ok so my heater/ac vents I dont believe are working properly, it is always comming out of the defrosters and never out of the dash vents no matter the setting, I checked a diagram and all my lines add up and are correct with the diagram, I when I mess with the gauges none of them even bother to try and move it seems, the only one that falls down is the one that lets the outside air in (it goes from being closed [not letting outside air in] to being open [no air hitting the passengers leg])

I am wondering if the valves are broken or maybe my ac/heater selector what do you guys think? and the heater doesnt really get warm even on the defrost, it is a new heater core only a year old could it just be because the vent doors arent working properly so all the cold air is being let in?

 

Defrost is the "default" setting.
So... "no vacuum = defrost".

I had this same problem you are and if I messed with the flapper-doors
they would try to hold their new position but couldn't really. The biggest
most powerful vacuum motor is the one contolling the fresh air door like
you were talking about. Hmmm... seems like it could hold its door?

Anyway... I bought a hand-pump to test vacuum-systems with. :)

Figured out I had a vacuum leak in the "can of tomatoes" under the hood. :/
It had rusted... as if it'd been opened with a can opener 1/6 of the way
around. Soldered it shut easy as anything.

I thought for sure my vacuum motors had gone bad and did quite a bit of
dismantling in the process of "proving" that to be true. Ooops. :)

Talk about making my engine idle and run better! ;)
That vacuum pump was worth the money.

Alvin in AZ
ps- if that sucker could rust out here it could rust out anywhere ;)

 

thanks alvin, I will take a look at it today.

is this what you are talking about btw ?

http://i6.photobucket.com/albums/y24...n/PA220023.jpg

Because, I have always wondered what in the world that was...lol

 

I don't know what that is either! LOL :)
Something to do with the air pump?

"can of tomatoes" is a name for it that I picked up off FTE. :)
Like a large can of tomatoes, label removed and painted black.
Or sometimes bigger and looks like a can of tomato juice. ;)

Maybe you aren't recognizing it because yours is the black-plastic "soft ball"
type of vacuum reservoir instead of the simple "can"? If that's the case then
that prob'ly ain't where your problem's at anyway.

To me the main trick is to find your vacuum leak.
That's where my "vacuum system testing tool" paid for itself.

Without it I would have bought a couple vacuum motors only to find out
they weren't the problem.

Mityvac

Borrow one if you can. :)
Your problem may not be a vacuum leak. :)

Using the hand-vacuum-pump is like hunting electrical trouble with a meter
instead of changing out parts one at a time. Can a guy really figure the
method of swapping out parts until you find the trouble anything other
than "a dangged stupid way" to do things? ;)

Another way to do it is to isolate various parts of the vacuum system.
The vacuum system tester will be easier and more straight forward.
What parts are good will prove themselves, like my vacuum motors
and dash-vacuum-switch did. :)

Alvin in AZ

 

Start it up with the heater on and feel the heat in heater core's hose as it
begins to work. Is the water control valve opening? Mine rusted shut right
after the pickup went out of warranty. :)

Heck, it still had the original antifreeze in it! :)
And no... I hadn't added tap water.

$40 for a new vacuum operated valve in 1976.
http://www.panix.com/~alvinj/file12/bypass.jpg

I put a gate valve in the hose and later switched it to the ball valve. :)
Yeah, I have to open the hood to turn the heater-core-heat on or off.
That's only a few times a year anymore. :)

I use the A/C in the winter here more than the heater.

YMMV

Anyway...
Your heater hose valve may not be opening from not enough vacuum too? :)

Alvin in AZ

 

I had the exact same problem. Last week I removed the hvac controls and the bottom lever switch, a vacume switch was broken. It's held in place by two screws, a vacume fitting and a three wire connector. I found a replacement locally in a private salvage yard. I replaced it and was good to go.

 

everything worked flawlessly today.. started the truck up let it warm up and prayed to god the heater would work (it was 22 degrees out my windows were forzen) and it did, the normal ducts worked too everything seemed fine, so it might be like what alvin said and be that gate valve because God i know that things never been changed out, its as old as that truck ahah

 

That is a pollution control valve. The hose going off to the left is going to the air pump check valve.