defog thru vents

My 1998 s-10 blazer has the defrost coming out the front vents. Actually all the air and heat is doing this. I didn't find a vacuum leak. Could it be the switch that changes from AC Bilevel vent heater & defog. I sure could use help with winter fast approaching.

My 1998 s-10 blazer has the defrost coming out the front vents. Actually all the air and heat is doing this. I didn't find a vacuum leak. Could it be the switch that changes from AC Bilevel vent heater & defog. I sure could use help with winter fast approaching.

Welcome to AF
Auto or manual ac/heater controls?

It is usually cause by weak or no vacuum from engine to heater controls.

Get a vacuum gauge and check for weak or no vacuum from engine to heater controls and check vacuum tank and lines for unpluged or broke.