I just figured I would pass this little bit of info that I learned yesterday. I was browsing through the owner's manual for my truck which I never even bothered to look at before and found some good info about the heater. I've always had the heater aimed at the floor and my feet would sweat and the window would be a bit icy or would have it on defrost and I would be sweating trying to keep the windshield clear. Well according to the owner's manual if you put the switch in between where it says deforst and floor it gives you the option of having some heat out the defroster vents and some aimed to the floor like you can on new cars. I never knew this before and figured some of you may not either since it is not marked on the controls. I think it is great because I use this feature a lot when driving other cars so it is nice to know I can do it in my truck now too.

Known this since day 1.

Good post though.

Thanks. I wish I know this the past winters I drove it. lol

Until you mentioned it Sean, I didn't know that either...I just assumed that you went directly to the marked spot on the lever!

That's what I thought too. You would think they would have marked it. I wonder how many people have been driving around for years like me not knowing lol.

Probably more than people will admit to...

I found out by accident that it worked that way.

When you put it half way between the two spots, you can hear the vacuum pull the flap half way open.

fatherdoug said:

When you put it half way between the two spots, you can hear the vacuum pull the flap half way open.

Click to expand...

Not on a dent. It's all cable actuated, no vacuum involved.

-Jared

Baitshop said:

Not on a dent. It's all cable actuated, no vacuum involved.

-Jared

Click to expand...

I think there is vacuum involved. There is a vacuum solenoid mounted on the heater box.

I think the heater valve is cable operated but the doors do work on vacuum. I wonder if it makes a difference as to whether it has the basic heater or those with A/C?

Mine has two cables. I think ones with a/c have vacuum and that probably would make it easier to notice the door opening at the halfway point.

I think you are right Sean...without A/C is all cable actuated.

DNFXDLI said:

I think you are right Sean...without A/C is all cable actuated.

Click to expand...

Yes, I didn't think about the differences between a/c and non/ac.

My dad first showed me this trick in the old '78, so I've used it for years. But, I did think that is was just "trick" that people figured out until I read the same thing Sean did in the owner's manual. I was surprised to see that it is an actual setting.

I stumbled across this by accident as well...but still didn't know it was planned to be that way...just figured something was wrong, but in a way I liked...haha.

Heater Only:

Those marks are only to mark FULL ON.
Because of the cable function especially thee doors move per lever adjustment and gives one portions of each option


as opposed to the AC controls

Only 1973/79 F100/350's (1978/79 Bronco's) with factory installed integral A/C have a heater water valve. It's vacuum controlled, spliced into the heater hose behind the air cleaner.

It's also been a POS since day one, notorious for getting stuck open/closed/halfway.

D4AZ-18495-A (replaced D1AZ-18495-A) .. Heater Water Valve (Motorcraft YG-136) / Available from Ford.

With factory installed integral A/C, mounted on the backside of the A/C-Heater control panel is this little charmer:

D5TZ-19B888-A .. A/C Vacuum Control Selector Valve Assy (Motorcraft YH-285) / Obsolete

This valve includes the 'kicker switch' for the compressor. All the A/C-Heater vacuum hoses for the water valve and the damper (blend) doors connect to this valve.

On each damper door is a vacuum motor.

Ha! I've now found the one good thing about dealer AC! I DON'T have the heater valve! I've got cables !
Dak