HVACR UNIT 13

In which system does less refrigerant enter the cylinder for each compression cycle, requiring more horsepower for each BTU of cooling?

A low-evaporator-temperature system

Which compressor has a piston that is driven up and down in the cylinder by a connecting rod and crankshaft?

A reciprocating compressor

Which compressor type draws refrigerant gas in through the inlet port into voids created by turning rotors?

A screw compressor

How does a two-step scroll compressor achieve capacity reduction?

An internal rotating plate opens and closes two drilled ports in the scroll.

All refrigeration compressors are designed to pump:

Only vapor.

An advantage of open drive compressors is that:

The motor and compressor can be replaced separately.

Which of the following compressors is NOT considered a positive-displacement compressor?

Centrifugal

Rotary compressors are commonly used in:

Window units.

Which of the following has the capacity range for a centrifugal compressor?

Commercial AC

The small gaps between the screws on the screw compressor are sealed by:

Oil flooding.

The major types of compressors listed by mechanical design are:

Reciprocating, rotary, scroll, screw, and centrifugal.

A compressor that uses an impeller to throw refrigerant from the center outward is a:

Centrifugal compressor.

A common application for centrifugal compressors is:

Commercial water chilling systems.

One technique for improving efficiency and comfort through compressor selection is to select a:

Compressor with capacity control to match the compressor capacity with the refrigeration load.

What type of compressors contain the compressor and motor together inside a welded steel housing?

Hermetic compressors

How does a reciprocating compressor operate?

In a reciprocating compressor, the piston is driven up and down in the cylinder by the connecting rod and crankshaft.

The match of the motor and compressor inside a hermetic compressor:

Is specific for the application of the compressor.

The shaft seal on an open compressor is more complicated than the gaskets and seals on other parts of the compressor because:

It must seal a shaft that is turning.

Which of the following is TRUE of a medium-temperature refrigeration unit?

It requires 1 hp to produce 2/3 ton of cooling.

Compressor cylinder unloading reduces the capacity of a reciprocating compressor by:

Making the valves in the head inoperative.

Refrigeration needs on trucks, tractor trailers, and shipping containers are met by:

Open-drive compressors.

What opens and closes the valves in a reciprocating compressor?

Pressure difference across the valves

The function of the compressor in the refrigeration cycle is to:

Raise the pressure and temperature of the refrigerant.

A compressor that uses a large off-center rotating shaft and multiple blades that follow the cylinder walls as the shaft rotates is a:

Rotary blade rotary compressor.

A compressor that compresses gas between a fixed spiral and an orbiting spiral is a:

Scroll compressor.

Three different design screw compressors are:

Single screw with gate rotors, dual screw, and triple screw.

An oil slinger is used with reciprocating compressors that are lubricated by:

Splash lubrication.

A compressor that uses an offset rolling piston that seals against a blade that remains stationary and moves in and out of its slot to seal against the rolling piston is a:

Stationary blade rotary compressor.

Assuming they both have the same condenser temperature, which application requires more horsepower to produce a ton of cooling: a 0°F evaporator, or a 40°F evaporator?

The 0°F evaporator, because of the higher pressure difference

The space left between the piston and the valve plate of a reciprocating compressor when the piston is at the top of the cylinder is called:

The clearance volume.

What is the lowest percentage of full capacity that a digital scroll can be safely operated for extended periods?

The minimum capacity is 10% to ensure that the compressor gets proper lubrication.

The advantage of compliance in a scroll compressor is that:

The orbiting scroll can separate and unload to pass a small liquid slug.

How can semihermetic compressors be characterized?

They have a bolted housing that encloses both the compressor and motor.

How can hermetic compressors be characterized?

They have a welded shell, which holds both the compressor and motor.