Final answer:
A variable displacement compressor is the type of A/C compressor that uses a control valve to alter system pressures.
Step-by-step explanation:
The type of A/C compressor that uses a control valve to alter system pressures is called a variable displacement compressor.
This type of compressor adjusts the displacement of the compressor based on the cooling demand of the system. By altering the system pressures, it can effectively regulate the amount of refrigerant flow and provide more precise control of temperature inside the room.
One example of a variable displacement compressor is the swash plate compressor, which uses a swash plate mechanism to vary the refrigerant flow by changing the tilt angle of the plate.