Oklahoma Refrigeration Journeyman

ACR tubing is sized by its actual outside diameter, while copper water tubing nominal size equals the OD minus 1/8 inch.

Galvanized pipe is zinc-coated and used primarily in water systems to prevent rust, while black pipe is less expensive and used for gas lines and non-water applications.

The defrost valve delivers large quantities of hot gas to rapidly melt evaporator frost, while the bypass valve meters only small amounts of hot gas to protect the compressor under low-load conditions.

A current relay coil is wired in series with the run winding and responds to high inrush current at start-up, while a potential relay coil is wired in parallel with the start winding and responds to counter EMF as the motor accelerates.

A single screw compressor uses one main rotor meshing with two star-shaped rotors, while a twin screw compressor uses two intermeshing helical rotors.

In a stationary-blade (divider-block) rotary compressor the blade is mounted in the housing and spring-loaded against the rotor, rather than being mounted on the rotating shaft.

A PSC motor uses only a single run capacitor for the entire operation with no switching relay, while a CSCR motor uses both a start capacitor (switched out at 60–75% speed) and a run capacitor that stays in the circuit permanently.

A stuck-open centrifugal switch prevents the start winding from energizing so the motor cannot start, while a stuck-closed switch leaves the start capacitor in the circuit continuously, risking overheating.

Halide torches and electronic detectors give false positives near urethane foam insulation because the foam contains refrigerant-based expanders, while a bubble solution relies on visible bubble formation and is reliable in that environment.

Three-phase power provides constant power because the three voltage signals peak at different times and never all reach zero simultaneously, resulting in less power loss at the transformer compared to single-phase power.

A range adjustment shifts both cut-in and cut-out values equally in the same direction (keeping differential unchanged), while a differential adjustment changes cut-in and cut-out by equal amounts in opposite directions (keeping average temperature unchanged but altering cycle length).

A low-pressure motor control's differential adjustment affects only the cut-out pressure, while a high-pressure motor control is a safety device set to cut out the compressor at 20% above normal head pressure.