GMC Repair: defroster, small screws, gmc suburban

Question
QUESTION: 1999 GMC suburban--- defroster inop.

ANSWER: front or rear????
If front,  do the other blower settings work (panel, floor, or bi)?


---------- FOLLOW-UP ----------

QUESTION: It is the front defroster.1999 GMc suburban 350 V8. You can hear a slight change in sound when put in defroster but air still comes out the botton like it is still on heater. I looked under hood for vacum lines that might be loose but all were allached as best as I could tell.

Answer
Hi
MOST likely it is the Mode door actuator, located on the drivers side, above throttle pedal area.
If you look up in this area, you'll see the actuator attached to the HVAC case. Should be just above and alittle to the right (passanger side) of the throttle pedal.
Held on by 3 small screws.
These vehicles ALSO have a BAD problem with the HVAC controller. It CAN cause this problem but MOST of the times there are numerous problems if it is the controller.
I really hope this helps.
Follow post back, if needed.
PAwl