Over the past few days, I've been trying to get the vent system going on my 79. Based on what I've read here: https://www.ford-trucks.com/forums/1...am-needed.html I have everything hooked up properly except for the hoses that turn off the water flow to the heater core, which are dangling freely.

BUT, when I run through all the positions, none of the actuators work well enough to actually divert any air to the floor or the vents.

The one that comes closest to working is the fresh air diverter over on the right hand kick panel; it mostly actuates but still needs help. With help, it'll hold the door all the way open but it can't make it there alone.

I can kinda-sorta feel some air coming out of the dash vents, but the majority exits the defrost area regardless of the selector setting.

All of my actuators hold vacuum when I hook them to my hand-held pump, but dont actually move freely enough to do anything when the selector is moved away from "Defrost."

These are run off of a vacuum pump, not engine vacuum, and at idle I have about 20" of vacuum so it should be plenty.

Is there any maintenance that I should know about before I try to replace these things? If replacement looks like it's the reasonable option, what is the proper name for these things? Rock Auto doesn't have a "Vacuum actuator," or anything that I can tell is close in their AC section.

It seems like there should be some O-rings or packings inside the dash selector, but I dont want to tear into that without knowing for sure if it's serviceable.

 

You talking about these? Here you go for a source.

Ford HEATER AND A/C - 57-79 Truck, 61-67 Econoline list - CG Ford Parts and Heater Temperature Regulator Valve

Click on the r/h ac stuff and it opens a page for the a/c heater vacuum temp regulators.

Cruise the site lots of good stuff. Anything else you might need off my 79 parts bronco with a/c and all the dash stuff still in it let me know.

 

The part listed is what I was curious about rebuilding. I may pick one of those up, but I'll have to do a little more investigating to see if there is actually a leak involved there.

The parts I was curious about possibly being weak are the little cans that the vacuum hoses connect to in order to close or open the various air passages.

I went under there and tried to free them up...they are moving a little, but I'm not sure how much travel they should have. Maybe I need to pull the whole box out again and put some weather seal around the doors inside. When I see them moving, it's just not enough to divert the air, so that could be the issue.

Sure wish I would have thought about that when the box was out of the vehicle...what a pain, getting that in and out.

Thanks for the link, though...that's a great site that I hadn't seen before!

 

Here to help with alot of free time on my hands, but my getting back to wrenching days are just around the corner.

 

1973/79 F100/350 & 1978/79 Bronco with factory installed integral A/C:

Has a vacuum controlled heater water valve (D4AZ-18495-A - Motorcraft YG-136), that splices into the inlet to heater core heater hose.

It's a notorious POS, gets stuck in the closed or open or partially open positions.

Each blend door has a vacuum motor (18A318) and on the backside of the A/C heater control panel is this little charmer:

D5TZ-19B888-A .. A/C Vacuum Control Selector Valve Assy. Includes the 'kicker switch' for the A/C. All the vacuum hoses attach to this valve, then to the blend door motors and POS heater valve.

When you slide the lever on the control panel, this valve opens one door, closes another. The hoses tend to crack where they connect to the nozzles on the motors and valve. They also tend to kink.

1978/79 Bronco with factory installed integral A/C:

 

couple of things, if you claim to have 20" of vacuum, use your hand pump to pump each individual diaphram, stop at 20" and see if that operates the lever. IF it does then you have a leak in the system or a bad selector valve. If it doesn't move the lever then the door is too tight and you need to open the box up and free it up.

Also, not sure if you have it, but a vacuum storage can and a check valve is a really good idea in a vacuum control system. IF you don't have one, the easiest unit is the old GM can, black plastic about the size of a softball, that has the checkvalve built into the can.

 

All 1973/79 F100/350's & 1978/79 Bronco's with factory installed integral A/C came w/a A/C vacuum reservoir with built in check valve.

 

Which part is that? The reason I ask is because I swapped in AC and don't think I got that part. My vacuum line runs from the manifold right through the firewall to the selector

 

D6TZ-19A566-A (replaced DODZ-19A566-A) .. Vacuum Reservoir / Obsolete

Use with factory installed integral A/C or High/Low Comfort Vent System: 1973/77 F100/350 / 1978 F100/350 & Bronco before serial number AJ0.001 / 1976/77 & 1978 Econoline before serial number AJ0,001.

Use with factory installed integral A/C: 1970/73 Maverick/Comet / 1971/73 Pinto/Bobcat.

Upper pic: 19A566

 

And i just noticed my speedo cable is too long...

 

Thanks. I will have to go and find one

 

Some look like a round plastic ball.

 

Just a late follow up, since I can't get to the truck every day:

It seems like the lack of air is mostly being caused by a failure of the selector doors to seal and that pulling it out again is going to be my best bet.

After a few days of cycling the actuators, they seem to have full range of movement.

The vacuum pump that I mentioned above is, of course, not a stock item but is there none the less. It's been reliable so far and was installed during a diesel swap. Having high, consistent vacuum has helped in getting these things excersized enough to work properly again.

Thanks for the replies!!

 

So the seal around the doors turns out to not be the problem.

I removed the box and inspected the actuators; after a little digging, I found out they are two position actuators, which would explain why they have two nipples sticking out of them.

Vacuum applied to the plastic nipple on each actuator gives enough movement for half of the normal range of movement, judging by the rub marks inside the box where the doors have moved in the past.

Vacuum applied to the second nipple, the metal one, produces no movement; no loss of vacuum as measured by my hand pump.

Vacuum applied to BOTH nipples still produces half normal movement.

Even with some pretty sever pressure applied to the actuator rod, full range of movement isn't happening.

Now then: Is there a source for reproductions? LMC, the above link, JBG, AutoZone, PepBoys, and any other place dont have them and I'm not getting any hits on the part numbers listed in the pictures above. The part numbers I'm finding are very similar, but have some extra letters or numbers tossed in and are for much newer vehicles, so I dont think they'll work.

E-bay has a few but they are either new/old stock or pulled from a vehicle and could have the same problem. Sellers confirm they have movement, but it may be the same amount that I have.

 

Are those numbers the original part numbers from ford?