I am working on getting the HVAC functioning in my '82 F150. I have some things working now, but I have a new issue today. Initially, all I could get was hot air through the defrost and could not shut off the blower entirely (but could change intensity otherwise). I believe that I have re-attached all of the related vacuum under the hood (please correct me if I am wrong). The blower switch and temperature control function. I don't know what I did, but after messing with it today it will now NOT blow through the defrost and the floor. I looked in my Haynes, but it seems to provide very little regarding these parts. I removed the vent control assembly from the dash. I was able to change from off to on modes, but not floor and defrost. I did find that the vacuum was audible in some positions, but not all. I was able to pinch the hose and the sound would cease. This makes me think that something plastic in the control assembly or the hose adapter is damaged. Is this related to the function selector in the dash, a motor, a sticking door or something else entirely? Any insight or suggestions would be GREATLY appreciated!


Under hood vacuum on passenger side


I don't know what to say about that check valve. Maybe it is a problem?


Vacuum hoses behind glove compartment


Vacuum hose joint behind dash

Cold air motor?


Other motor?



Vacuum hose adapter to the control assembly





The hose that I am pointing at seems to be the primary vacuum coming from under engine compartment

 

The vacuum system on factory A/C trucks works essentially the same for '80-86 & late '88-96 (NOT '87-early '88). Click these, read the captions, & follow the relevant links:


(phone app link)


(phone app link)


(phone app link)

But you can find more-specific info about that control valve on Garagemahal's Resources forum, in the A/C writeup threads.

The vacuum hose to the recirculate door motor (first pic) is NOT connected properly, or long enough. So it's not the check valve that's the problem.

 

Thanks Steve. I pulled the gasket on top of the blower motor case and found that the white vacuum line was severed. You said that the hose to the door motor was not connected properly... The link for the second picture you linked was the only one with any description about this. It says that the black vacuum hose goes to the "T" with the check valve and then to the vacuum reservoir. It says that the white vacuum hose is the one that goes to the actuator. Does this seem correct? Thanks again!

 

I hooked up those vacuum lines so that the white line is going to the actuator next to the firewall and the black to the reservoir "coffee can". This had no effect on the functionality or lack there of. What should I try next? Is there any reason to believe that the vacuum selector assembly could be part of the problem?

 

Until you confirm ALL the vacuum lines are connected properly, you can't diagnose anything else. The most-important is the black line, but it's also critical that the coffee can is NOT leaking (which they invariably do at this age).


(phone app link)

Yes, the control valve can fail due to its grease drying out (either from age, or dust when the coffee can fails), and I think it can be disassembled, cleaned, & greased (but I've never tried).

 

I tested the coffee can reservoir with a mityvac by putting on 15" Hg and waited 5 minutes to see if the pressure dropped. It didn't at all, so I think it is safe to assume the reservoir is still functional.

I traced all the lines again and according to that one schematic they seem to be in proper order. Again, correct me if I am wrong.

I tried to troubleshoot the actuators themselves with the mityvac. The blue one (floor/panel) works without problem. The red/yellow (floor/defrost) actuator arm hardly moves, even when I put 20" of pressure on it. I would presume that to be the problem, however, I am able to manually move the arm and thus the door (I can hear it move in the vent) and it still doesn't change from the panel vents. I attempted to apply vacuum to the recirculating motor as well, but it wouldn't hold at all.

I have taken the FCCB out and as apart as it gets. I am not sure how it should be greased, if at all honestly. I would rather spend my time studying, but I will obviously need the defrost come winter.

I am at a loss...

The replaced vacuum hoses. The one going to the recirculating motor IS the white line now. The other is the black to the manifold/reservoir "T" valve.

I see the tiny holes on the tan plastic piece that presumably go to the individual ports. Where should I apply grease?

 

I have no way to check them since you used black for everything, and your pics don't show enough for me to check.I assume you mean 20" of vacuum, but you didn't specify which port on the vacuum motor you applied that to. One makes the motor move 1/2-way (defrost to mix); the other makes it move fully (defrost to floor). Study the HVAC vacuum system diagram.Depends which one you're moving, and where the other one is.Then that's the main problem - it's dumping all the vacuum, so nothing has enough force to work.That doesn't look right to me. The check valve is its own "T". There shouldn't be a 2nd "T" after the check valve - nothing else in the system gets constant vacuum; just the reservoir & control valve.To the thin sharp edges of the chambers on the black disk that ride directly against the tan valve. NOT enough to plug any of the tiny holes; just enough to create a "liquid" seal between the black & tan plastic surfaces.