Unit 13 - HVAC

What type of classification applies to a hermetic compressor?

• Mechanical design

• Cooling mechanism

• Displacement

• Physical enclosure

Which of the following compressors is classified by mechanical design?

• Ultralow

• Positive displacement

• Centrifugal

• Open

How does a dynamic displacement compressor cause an increase in refrigerant pressure?

• By pushing the gas out of a space with a piston

• By creating a surge in the compressor

• By blocking the discharge port of the compressor

• By speeding the refrigerant up to a high velocity

Which of the following statements BEST describes the difference in the way positive displacement compressors and dynamic displacement compressors move the refrigerant?

• A positive displacement compressor pulls the refrigerant out of a space, whereas a dynamic displacement compressor pushes it out

• A positive displacement compressor pushes the refrigerant out of a space, whereas a dynamic displacement compressor pulls it out

• A positive displacement compressor pushes the refrigerant out, whereas a dynamic displacement compressor throws it out

• A positive displacement compressor throws the refrigerant out, whereas a dynamic displacement compressor pushes it out

Which of the following describes a similarity of open compressors and semi-hermetic compressors?

• The valve plates of both types of compressor are field serviceable.

• The motors of both types of compressors use a shaft seal that is subject to forming leaks.

• The motors of both types of compressors are enclosed in a steel shell.

• The motors of both types of compressors are separate from the compressor.

The motors of both types of compressors are separate from the compressor.

• They have a lower sound level

• They have motors that are separate from the compressor

• They use a shaft seal to prevent refrigerant leakage

• They can be made in larger sizes

Which type of compressor uses an orbital component to trap pockets of refrigerant and decrease the size of those pockets in order to increase the pressure and temperature of the refrigerant?

• Screw compressor

• Reciprocating compressor

• Scroll compressor

• Rotary compressor

Which of the following BEST describes the operation of a centrifugal compressor?

• They use a crankshaft and a rod to move pistons up and down in a cylinder to compress refrigerant

• They use one fixed scroll and one orbital scroll to capture pockets of refrigerant and gradually decrease the size of those pockets

• They use an impeller to throw refrigerant into a snail shell-shaped scroll that directs the refrigerant toward the compressor

• They use a rotor that turns within a cylinder and progressively compresses the gas in the rotor spaces

Which of the following best describes the method typically used to cool an air-cooled compressor?

• The condenser fan airflow blows over the compressor

• The refrigerant gas is passed over the motor before it enters the compressor

• The condenser water line is wrapped around the condenser fan blades

• Outside air is blown over the condenser water line

Why can a refrigerant-cooled semi-hermetic compressor operate at a lower superheat than compressors cooled by other methods?

• Because outside air is pulled into the compressor

• Because a dedicated fan is not needed to cool the compressor

• Because the refrigerant goes over the motor before entering the cylinders

• Because the temperature and pressure of the system are higher than in other systems