ok so its been a while since my last post but here is my issue:
when I turn on my heater after the engine is at normal temp i turn to full heat and i can hear the fan working but the defrost setting barely blows any air at all if i switch to cold it blows alot. also if i switch to the foot setting it blows more air than defrost and so on ive pulled it all apart and cant see anything wrong yet... without tearing all the ducting apart i have a 1990 civic if anyone has any ideas or if this is a common problem please help

 

If you don't have air conditioning, it's pretty simple to remove the duct between the fan and the heater box (installed behind the glove compartment where the evaporator would be if you did have A/C). From there you might be able to see if the heater core is clogged with leaves, etc. Also check that the air doors are actually moving like they should when you move the controls on the dash.