Aircraft Air Conditioning System

Vapour Cycle Air Conditioning System

• The receiver-dryer serves as a reservoir for the liquid refrigerant and filters out moisture from the system.
• It is located in the high side between the condenser and the expansion valve.

Compressor and Refrigeration Cycle

• The system is divided into two sides: the low side (accepts heat) and the high side (disposes of heat).
• The compressor increases the pressure and temperature of the refrigerant vapour.
• The refrigeration cycle starts at the receiver-dryer and flows through the expansion valve, evaporator, and compressor.

Evaporator and Cooling Process

• The evaporator is the unit that produces the cold air, where heat is absorbed by the refrigerant.
• Warm air is blown through the thin metal fins that fit over the evaporator coils, and the heat is absorbed by the refrigerant.
• When heat is absorbed, the refrigerant changes from a liquid to a gas without increasing its temperature.

Refrigerant and System Requirements

• R134a is the exclusively used refrigerant in aircraft applications due to its low environmental impact.
• The refrigerant must be highly volatile (high vapour pressure and low boiling temperature).
• Only the refrigerant specified in the aircraft manufacturer's maintenance manual should be used for servicing the system.

Importance of Moisture Removal

• Moisture must be removed from the system, as a single drop can freeze in the expansion valve and stop the entire air conditioning process.
• Water reacts with the refrigerant to form hydrochloric acid, which is highly corrosive to the metal in the system.