Are there two blowers for the front heating system? One for the floor (under dash) and another for the dash vents?

I get heat coming down under the dash but little from the dash vents with switch set to MIX.

If not, how is that controlled?

Also, should the rear heat blower be running when the dash controls are set
to Cool | AC?

 

You don't mention what year van you're dealing with, but usually, there's only one front blower motor, with a moving door damper system to redirect the air flow to the various vents. The damper door is vacuum controlled by a switch controlled by the selector lever. The "mix" position has the damper stop in between to closed positions, so heat is allows to flow both to the floor outlets, and the dash outlets.

When in this position, air flow is much less, since the total CFM is divided between two targets.

The rear motor is controlled by a separate blower control switch, so it could be off when the dash selector is in Cool|AC.

 

My van is a 1999 E-350 Super Duty.

Seemed like there was way more heat coming of the dash vents out last Monday when I looked at the van than yesterday.

Can I see the system if I remove the "dog house" engine cover? Are there electric valves to control the vacuum and maybe a fuse involved?

 

Probably not, it's located behind the dash. You can't see any of it on my 89 from the doghouse area.

Last week, I had the controls out of mine to seal up a small vacuum leak, accessibility isn't too bad.

On my 82, the foam rubber seal on the damper door disintegrated, causing all kinds of air flow issues, so I removed the dash, and heater control box, and rebuilt it completely when some neoprene. Worked great, but that's a LOT of work.

 

So what is the dash switch doing? How does that selector affect a change
in the vacuum?

 

This is a vacuum switch, the red, yellow, and blue "wires" aren't wire, they're little tubes. Inside the "switch" is a small block, with machined grooves that changes which tubes see vacuum.

The other end of these tubes are connect to little vacuum motors. The vacuum motor, is just a can with a diaphragm that moves when vacuum is applied, connected to a level that moves the door.

Leaks in this system mostly causes things to "relax" to their natural, or spring based "parked" position. The most common complaint is that the "air" shifts to the defrost vents when accelerating, since the engine loses vacuum under load, and if the vacuum system bleeds, then the "motors" park.

This is the vacuum system diagram for my '89.

 

Yikes! Very interesting. Thanks for taking the time to answer this.

Will try and post back when I've had a chance to take a peak inside.

 

See this thread also, it has a diagram that should be more like your '99

https://www.ford-trucks.com/forums/1...vents-eek.html

 

Feel foolish on this one. I tried the heat again last night and found I had the switch set incorrectly. I thought the setting for "vent" was just for fresh air... not heat.

Anyway, when I set it to vent the heat came pouring out from the dash. Silly me.

Sorry for the bother. Appreciate the helpful pics and explanation of how the heating system actually works.

 

We learn by asking Scooter! Its been said there are no "dumb questions" but there sure as heck are MANY dumb mistakes (from NOT asking) !

I'll also suggest you get over to FleaBay and look for an EVTM aka Wiring Diagrams book: 1999 Ford Econoline Club Wagon Wiring Diagrams | eBay Not only does this help in your future repairs it helps acquaint you with the various control systems your van his. Don't be concerned that some of these are listed as Club Wagon specific. Such manuals are not that vehicle model specific---they'll work perfectly on the more basic models too.

HTH