Blower Fan

• The blower fan for the air conditioner and the heater is behind the glove compartment in front of the passenger seat. If the bearings for the fan are worn, it may squeak while it's spinning. If the sound continues consistently whenever the AC or heater is blowing but stops when the fan selector is switched to the off position, then the blower fan may need to be replaced.
  
  

Vent Selectors

• The climate control system uses actuator motors to move louvers in the vent system to select between the different vents on the dashboard. When you turn the selector from "Feet" to "Face," the actuator moves and the air is routed to a different channel in the vent system. If the squeaking sound only happens when you select a different vent, then the actuators are the likely culprits.
  
  

Recirculation

• Vibes use a different set of actuators to switch the air flow from using recirculated air from within the cabin of the car to using fresh air from outside the car. Using recirculated air also tends to increase the coldness of the AC since it cools the air, and then recirculates and further cools the air. If the squeaking happens when you press the recirculate button just below the AC button, then the actuators for the recirculation system are failing and need to be repaired or replaced.
  
  

Compressor Belt

• The belt that drives the AC compressor also drives the engine cooling fan under the hood. It wends its way between the components on the passenger side of the engine. As the belt becomes worn, it may slip on the various twists and turns it makes around the fan, generator and compressor; and the slipping will cause a squeaking or squealing sound. You can differentiate between the blower fan and the belt by listening to the sound with the hood open. The squeaking will be much louder under the hood than in the cabin of the car. The squeaking will also occur when the engine fan is running, not only when the AC is powered on.