Chevrolet Repair: Heater\defroster not working, 1995 chevy corsica, chevy corsica

Question
Van, Hi I know that you work on light trucks but maybe you can help me I have a 1995 chevy corsica, that my heater\defroster won't work. the blower is working fine. The switch will turn to all points but air flow only comes out of the dash vents and slightly out of defrost for front window.The switch has been replaced do you have any Ideas that I can try. Also the cat sounds clogged could this be a factor.

thank you
jeff ( frozen if no help)

Answer
Hi Jeffrey,
I am not sure if your car has electronically controlled electric motors that operate the flow control doors in the heater system, or if they are vacuum operated.
If they are run by vacuum, a plugged cat could sure contribute to that, since it would reduce the vacuum due to back pressure, but I would expect it to be running terribly.
I would for sure be looking at the vacuum, weather that is the cause, or leaks.
Van