yz450pilot

I have a 2004 f-150 super crew fx4, and i just noticed my defrost stopped working. I have full air pressure coming from the vents but nothing comes out of the defrost when i switch it over. It is a manual climate control and i have done some searching for answers. Help would be great.

Mod (Ret.)

This may sound silly, but when you place the control (selector) to the defrost (dash vents) position, do you hear a vacuum leak? Placing your ear to the center or middle of the dash and listen for a "swish" sound would indicate a vacuum leak. If you don't hear a sound of air escaping, then I suspect you have a broken valve that opens/closes air direction from the main air duct (off of the blower fan) to the other duct work (i.e. dash vents, floor vents, dash vents for window defrost, etc.). The round dash selector routes a vacuum from the engine to operate various vacuum operated valves which in turn open/close, and route the warm (or cold air conditioned) air to the proper ductwork.

You either have a broken valve or a vacuum leak in the valve that opens/closes that duct system.

You may be able to remove the center plastic trim that surrounds the radio (and houses the 3 switches below the radio) using a flat blade screwdriver (or plastic trim tool), then start the truck and operate the switch that selects the vents (floor/dash/windshield). Removing the radio as well might gain some viewing site within the dash to locate the various valves the switch is routing vacuum to.

ktmmom189

I had this same problem, but it was the doors inside the dash that redirects the air to defrost, floor or vents. They have foam on the back of them and they had all fallen off so I could only get floor or vent. They had to dismantle the dash ac everything. Thank goodness it was under extended warranty