Heater/AC works, but defroster suddenly quit. Once when I restarted the truck it started working again, then when I turned it off I couldn't turn it back on again. Fan runs; I have no clue to the problem except that the windshield doesn't clear. Knowledgeable replies appreciated!

Year: 1998
Model/Trim Pkg:
2wd or 4x4: 2wd
Suspension setup: (bodylifts would be mentioned here)
Wheels:
Tires:
Pics:

 

Welcome to the forum

So the air is not blowing out the defrost vents under the windshield

That is odd since Defrost is the default setting on the system

Diagram here of the vent doors, at the bottom: https://www.ford-trucks.com/forums/a...ntid=517&stc=1

There are TWO
These two doors control direction of air flow to, Defrost, Panel, and Floor
They use Vacuum "motors", which are like solenoids, each door has labels, V for vacuum, NV for no vacuum, PV for partial vacuum
With NV at both doors air flows only to Defrost vents

My "guess" would be the Panel/Defrost door is stuck in the V position so maybe the spring in the vacuum motor is bad
Vacuum motors look like this: https://ww2-secure.justanswer.com/up..._explorer5.gif

Vacuum hose at one end and an Arm at the other end, Arm is hooked to a lever for the door, inside is a spring that pushes arm out to hold the Door in the NV position
When vacuum is applied the arm is pulled in so Door is now in the V position

So your Panel/Defrost door may be jammed, or vacuum motor spring can't push it to the NV position


And just FYI, the Blend Door(temp door) uses an electric motor not vacuum motor in 1995 and up Rangers
Only other vacuum door in the cab is for fresh(outside) air vent