The dash vents on my car do not blow out. They blow out on the windshield. on 1998 Oldsmobile Regency

I have had the car 3 yrs & they never have worked. was going to have it looked @ but had no idea what is wrong with it. It gets very hot in the summertime

2 answers
Most likely a vacuum leak under the hood /or do you hear a hissing noise from the heater selector area?
May leak there as well. See your mechanic, chances are good, not to expensive to fix!
ck for vac leak under hood near p/s of fire wall