ac damper door

trying to find out what position damper door should be in when ac is on. I have a 92 f150, and when truck is off, damper door is in a position where you can see the blower motor. when i turn on max ac, it stays open, when i turn on norm ac, it closes, and any heater setting or defrost, it stays closed. is this normal? ac not blowing cold, and low side reads 100 psi, high side reads 210 psi. any help would be great thanks.