I get no air through the defroster to the windshield. The other vents work fine. Is this a vaccum line problem, if so where might it be located?

A vaccume line is either cracked or broken.

Have the vents checked. See if there's a leak or something block the air passage.

sounds like the heater door actuator is bad, or a vaccum line came off of it.

This is a common problem on all Astro/Safari vans. The problem is a leak in the vaccum lines that control the vaccum switch responsible for changing air direction from the defrosters, dash vents, floor vents..etc.
Many of the problems that plaque the Astro/Sarfari vans and many other "Mini-Vans" is the build up of excess heat in the engine compartment. It\'s a tight place to put a V6-4.3 Vortec engine and the heat generated bounces back and cooks everything on the engine (coils, modules, sensors, wiring, and of course plastic vaccum hoses). No need to mess with your switches or anything behind the dash -- replace those thin plastic vaccum hoses to operate the vaccum switch (located just below the A/C canisters, to the right of the heater/ac blower housing) and your dash switches will magically send heated or cooled air where you want it.

may be a vaccum line check for a vaccum line that runs from the heater box under hood by fire wall hose or plastic line check to make sure its not off or for holes

I have a 1999 Ford Expedition Eddie Bower and my front heat does not work just blows cold air. The rear heart works fine any Ideas?

defrost dorr is not opening check to see if cable clamp has broken or if works off vaccum check for broken vacum line. berrydalewolfe

Hope you have the same set up, sure you do. You may have either crossed your vaccum lines or when you were putting your heater/ac box back together or you may of pinched the vents somewhat closed. Cycle through the different zones to ensure the vents are moving as your are selecting (defrost, floor, ect...) If you think the vaccum lines are correct then you may have a reassembly issue with the Heater/ac box. I had the same problem with my 2000 Dodge Ram 4x4. Use the KISS rule "keep it simple stupid" start with the vaccum lines and all your wiring to the motors, make sure everything is plugged in. Hopefully you'll find it there before going back into the box again.

replace the control unit.

Have you checked the diverter doors under the dash??
It sounds like a vaccum hose may have fallen off your vent controller.
I have had similar problems and found that the air WAS moving, but it was all going up through the defrost vents at the windshield.
A quick check of the vac. lines showed that one under the glove box was pulled off.
with the engine running, try setting the air settings to all the options ( vent/floor/defrost..etc..)
See it you can feel or hear the diverters moving under the dash..