Arizona R-39/CR-39 Residential and Commercial Air Conditioning and Refrigeration HVAC Contractor Practice Exam 2026 - Free HVAC Contractor Practice Questions and Study Guide

A compressor achieves positive displacement by changing the internal volume of the compression chamber. This process is fundamental to the operation of positive displacement compressors, which work by mechanically reducing the volume available to the refrigerant within the chamber. As the volume decreases, the refrigerant is compressed, resulting in increased pressure.

The principle behind positive displacement is that as the compressor piston or rotary element moves in a way that reduces the volume of the chamber, the gas is pushed out under high pressure. This mechanism ensures consistent flow regardless of the pressure fluctuations in the discharge side, which is critical for maintaining system efficiency and performance.

In contrast, while increasing the pressure directly might seem relevant, it is actually the mechanical action of reducing the volume that enables the pressure increase. Decreasing the volume of the system might suggest a broader interpretation that includes other aspects of a refrigeration cycle, but the direct relationship of changing the internal volume of the compression chamber specifically refers to how compressors operate. Cooling the compressor coils is unrelated to the mechanism of how positive displacement is achieved, as it pertains more to thermal management rather than the compressive action itself.