No Heat in 1993 Dodge Shadow?

Not sure what's going on with my usually reliable back-up car. My piece of crap Pontiac Montana is out of work right now, thanks to a probable blown head gasket. This leaves me with my, usually, trusty Shadow. Problem is no heat. We've bled the air out of the radiator, did a system flush, the thermostat is good, it has plenty of anti-freeze, the blower works great, which leaves me wondering why I have no heat. If you put your hand right over the vents you can feel a little warm air, but no matter how long you let the car warm up, it never warms up! The windows will defrost after about 20 minutes, but you can forget about being even a tiny bit warm. HELP!