I just purchased an 89 F-250 with a new engine.
It has the vacuum actuated a/c and heater controls.
The 'off' setting works just fine. All other settings only blow ambient air out of the defrost vents. I have checked all vacuum lines and they are fine - no leaks.
There are 5 lines.
BLUE - controls the panel vents (below glove compartment)
YELLOW and RED - seem to control the floor vents (behind radio)
WHITE - seems to control the flapper to the evaporator?? (upper left corner of engine compartment)
BLACK - what does it do??? it seems to mount to the side of the evaporator. There is a tee in the vacuum line - my real question is where should this tee lead to?? Right now it goes to the carbon canister (someone hooked these up wrong). Right now I have no source of vacuum to the heater controls or the carbon canister. Is it OK to just tee into another line off the intake manifold or throttle body.
Thanks for any help.

Floyd

 

there is a vacuum supply tank that operates your heater controls.

It is usually black in color, round and has two vacuum hoses conected to it and can be found under the hood.

there should be a lable that has vacuum routing.It should be on the core support or under the hood. Follow it for correct hose routing applaction.

have never seen heater controls work off a fuel canister!

fuel canisters are to pull fuel vapors from fuel tank and other smog controls and send back to engine to burn.

the carb. or intake is not where you should hook your heater control line into.

Find the supply tank and if you can't find it most shops would help you find it for free unless some shade tree machanic toss it.

good luck

gseeders

 

The black line originates at the manifold fitting (vacuum distribution source) located on the top of the upper intake manifold. It then goes to the vacuum check valve where it splits to the vacuum canister and the other line goes to the AC/Heater Function selector. This is the source vacuum line to the switch.

Mike

93' F-150 Ext Cab 5.0L E4OD, MSD, K&N, 31x10.50's

 

I have 95 f150 5.0 4x4,, bought it knowing it needed a wee bit of TLC,, which has turned into "The money pit". A grand learning experience it has been. So,, as to my query. Small vacume accuated control over the a/c system under the hood. When I move the control by hand I hear a Flap/door inside move. The very small white/ yellowish vac line is broken and continued to desinagrate when breathed on. I have no clue where it attaches., to get vacume from Any of you kind folks have a description and maybe a pic. that would be greatly appricated.

 

I saw nobody ever responded to you and I know it’s a old thread but did you get it fixed? I can give u diagram if not lol

 

On my 94 f150 on top of the heater blower there is a harness of wires and a white vacuum tube that goes to a flapper control. The white tubing is mostly rotted away. Wondering if I can splice into it to fix the bad part. There is no air conditioning.

 

yes you can, but it would be better to replace as much of it as you can.

 

Anyone know where the white tube goes to?

 

Bringing this back as i have a similar issue with the white line disintegrating. Wonder if anyone knows where it goes so i can replace the whole thing or do i have to try and patch it

 

Not sure if it’s possible to repair it. It crumbles when I touch it.

 

See if this helps even though its aimed more towards the 1992 and later years: E-Series HVAC Controls