Heater and AC only blows through the defrost and floor vents.
on 2003 Mercury Grand Marquis

The control button only reads floor and vent. Floor vent on driver side seems blocked, not much air.

Asked by for the 2003 Mercury Grand Marquis
3 answers
you may have a blend door issue seek a diag and est
you need to check your vacuum lines under the dash
Poss. MODE control motor.