In an air conditioning cycle, the coldest air is produced by the

• A. Expansion turbine
• B. Condenser
• C. Compressor
• D. Evaporator

Answer: (A)

In an aircraft air conditioning (air cycle) system, the biggest temperature drop happens when the high‑pressure, hot air expands through the expansion turbine. This expansion does work on the gas and converts enthalpy into shaft work, so the gas loses a lot of energy and its temperature falls sharply. That cooled air is what ultimately provides the coldest air to the cabin.

The other components don’t produce the coldest air in this cycle. The compressor raises the air’s pressure and temperature; the condenser (in systems that include one) rejects heat to the surroundings; and the evaporator cools cabin air by exchanging heat, but its exit temperature is limited by the cycle’s conditions and is not as low as the turbine exit.