my blazer heater works on all selections but the floor what do I look for to fix the problem I looked behind to glove box but don't know where the door for the floor is

 

These two actuators are on the driver side, just above the gas pedal. The lower one has two vacuum lines. Make sure they get vacuum, make sure the lines are connected, and the doors move when you change the mode switch position:




This chart tells what lines should have vacuum in each position of the mode switch: