1991 Heating Problems

When car is running, car does not over heat, warm air comes out of defroster vents only even when changing from defrost to vents. Heater core is good, fuse is good. Please help a cold friend.

You have a broken vacuum supply line somewhere in the system. Usually it is located below where the battery sits. You should be able to locate a vacuum hose (1/8" plastic) which runs from the intake manifold to the firewall and toward the driver's side. This hose should run to the reservoir hidden behind the splash shield in the wheel well and below the battery tray.

sorry, i had wrong info at first. Car is a 1991 Oldsmobile Cutlass Ciera. Does this change anything? And does this need to be moved?

Same answer.