Hi guys. Been here before as ‘93BLZR. I’m having a weird issue with my blend doors. Defrost works but also come from floor. If on MAX AC it comes from the floor and from the dash. Any ideas? Everything connected under hood. I have a hissing from the HVAC control.
1993 S10 Blazer

 

At least for the 2nd gen Blazers but likely for the 1st gen too, leaks in the under-hood engine-compartment vacuum hoses can cause this as they supply vacuum to both the front axle engagement and for the actuator doors for the HVAC system.