1990 Lumina

Have no heat, a/c working fine. Need the air to flow over heater core. Is there a flap that moves to direct the air? Have it torn down to the heater core. Can't seem to find it..

I don't think there is one, if the heater and evaporator cores are stacked together. It is probably your heater control valve.

If the heat is on, and the motor is running and warmed up, there should be equal heat in both hoses to and from the core. If not, the control valve is stuck, or the core is plugged up.

The heater core is hot, real hot just doesn't seem to be blowing air over or thru it. Have lots of air flow. Just is blowing over the a/c evaporator core. Car has been in florida for a year with the a/c on and heater not used. Thought maybe a door is stuck?

there is a temp control motor, located on the passenger side of the console that switches from hot to cold. It mounts with 3 screws, and is about 4" square, and is just above the clear vacuum valve assy. get your head under the dash and have someone move the temp control, you should hear the motor engage if it's working.

Yes found that and its not working. Manually opened the flap between the heater core and a/c evaporator. Either the motor is gone or the control center is not working. Thanks for all the feed back..