98 Explorer 5.0 V8 XLT heat and air thru defrost vents only?!>!

Hey there. I've got a 98 5.0 V8 Explorer XLT with 68k on it. I've got a problem with heat and AC where, regardless of the setting(heat/ac/floor/front vents/defrost), all air ONLY comes out of the defrost vents up front. The level does go up and down(both fan strength and hot/cold) when adjusted... basically everything works normal except it only comes out of the defrost vents... very frustrating. Any tips would be GREATLY appreciated. I'd prefer to fix it myself if possible(I'm hoping it's just a disconnected hose or something?). Any help would be greatly appreciated.

Thanks all!!! Matt

No vacuum , check for loose/broken vacuumhose under hood, passenger side

I agree, vacuum problem. When it comes out through the defrost, it is in "default mode", which happens when the vacuum does not work. Look in glove box, there is usually a manifold with vacuum lines.

Dead on.. I just recently had this problem and ended up tracking it down to one of the solenoids that control vacuum to lock/unlock the front axle. This would of course only be on a switchable 4x4 (not AWD). the solenoid had a hairline crack and was bleeding vacuum slightly enough not to hear it but enough to cause the problem. HTH

Steve