My defroster quit working and I heard what sounded like a vacuum leak coming from the heater/defrost/a/c control unit in the dash. I started trying to track down the leak and before I knew it (actually about 2 weeks later) I had my dash completely ripped apart and my heater box laying on the garage floor. My handy-dandy "mity-vac" brake bleeder pump confirmed what I suspected- the "heater blend door actuator" was bad. If your defroster isn't working and your vacuum lines are OK, this could easily be your problem as well. They're a bear to get to because the whole box has to come out. I hit RockAuto.com to do some shopping.
Heater blend door actuator- 28.79
A/C and heater control switch- 6.98
A/C Vacuum control valve- 9.65
My fan switch has been broken for several years, it was functional but the knob wouldn't stay on. The vacuum valve was cheap insurance. I'll try to clarify anything if I can. Just ask.