If you have the auto climate control system, its probably the heater
blend door problem.  The dealer fix involves the replacement of the
plenum which holds the blend door, which is buried under the dash, i.e.,
mucho dinero $$$$.

Some people have accessed the blend door by removing the glove box to
expose the plenum, and then cutting a hole in the front of the plenum,
and then fishing out the blend door and fitting in a replacement door.

My 96 Eddie Bauer Exploder has the same problem, and I'm waiting for a
free weekend to tackle the fix.

Larry