my 93 legacy has a heater problem. When it works it works great, but the problem is becoming more frequent. The temp gauge stays the same and you can feel warm air at the vents, defrost, etc. but it stops blowing warm air and blows cold air on the passengers feet. Blower motor still work on all 4 speeds when it does this, as well as vent, heat, defrost, etc. it just doesn't blow out of these locations. Don't really know where to start on this one. Thanks!