313A Compressors & Condensers

Question 1

What type of compressor uses pistons driven by a crankshaft to compress refrigerant?

Accepted Answer

Reciprocating (piston) compressor

Answer

A reciprocating compressor uses pistons connected to a crankshaft that move up and down in cylinders to compress refrigerant vapour, and is one of the most common types in commercial refrigeration.

Question 2

What is the main advantage of a scroll compressor over a reciprocating compressor?

Accepted Answer

Fewer moving parts, quieter operation, and higher efficiency at part load

Answer

Scroll compressors have fewer moving parts than reciprocating compressors, resulting in smoother, quieter operation and generally higher energy efficiency, particularly at part-load conditions.

Question 3

What is 'liquid slugging' in a compressor and why is it dangerous?

Accepted Answer

Liquid refrigerant entering the compressor cylinders, which can cause mechanical damage due to incompressibility of liquids

Answer

Liquid slugging occurs when liquid refrigerant enters the compressor, and because liquids cannot be compressed, the compressor valves and pistons can be severely damaged or destroyed.

Question 4

What is the purpose of a crankcase heater on a refrigeration compressor?

Accepted Answer

To keep the oil warm for easier starting in cold weather and to prevent refrigerant migration into the crankcase oil

Answer

A crankcase heater prevents refrigerant from migrating and condensing in the compressor oil during off-cycles, which would cause foaming and oil dilution on startup, potentially leading to bearing failure.

Question 5

In a hermetic compressor, how is the motor cooled?

Accepted Answer

By the suction refrigerant vapour passing over the motor windings

Answer

In a hermetic compressor, the motor and compressor are sealed in the same shell, and the cool suction vapour returning from the evaporator passes over the motor windings to carry away heat.

Red Seal HVAC 313A Practice Test

Red Seal HVAC 313A Practice Test

313A Compressors & Condensers