Tpc 433 Compressors

Question 1

A positive-displacement compressor uses a piston or other device to

compress refrigerant vapor in a chamber
force refrigerant vapor into a small tube
increase the volume of refrigerant vapor in a chamber
whirl refrigerant vapor at high speed

Answer 1

compress refrigerant vapor in a chamber

Question 2

Which of the following is a kind of kinetic-displacement compressor?

Centrifugal
Helical
Reciprocating
Rotary

Answer 2

Centrifugal

Question 3

Which of the following is part of a scroll compressor?

Helical screw
Impeller
Inlet Valve
Swing link

Answer 3

Swing link

Question 4

A multiple-stage refrigeration system has more than one

compressor
condenser
evaporator
receiver

Answer 4

compressor

Question 5

When selecting a replacement compressor, you need to make sure the replacement will operate (with/at) the proper

ambient temperature
discharge pressure
metering device
superheat

Answer 5

discharge pressure

Question 6

Among reciprocating compressors, the crankshaft is usually vertical in a(n) ____ compressor, but horizontal in a(n) _____
compressor.

full-hermetic; open
open; full-hermetic
open; semi-hermetic
semi-hermetic; open

Answer 6

full-hermetic; open

Question 7

On the pistons of reciprocating compressors, the ______ ring(s) prevent oil from reaching the compression chamber. The _____ring(s) prevent refrigerant from escaping around the piston during compression.

• bottom; top
• full set of; bottom.
• full set of; top
• top; bottom

Answer 7

bottom; top

Question 8

Which of the following is a method of distributing lubricating oil in a reciprocating compressor?

• Capillary action
• Crankshaft splash
• Vacuum lines
• Wicking

Answer 8

Crankshaft splash

Question 9

A cylinder unloader reduces the capacity of a reciprocating compressor by allowing refrigerant to flow through the ____ port during the ____ stroke.

discharge; compression
discharge; intake
suction; compression
suction; intake

Answer 9

suction; compression

Question 10

One way of reducing vibration problems in reciprocating compressors involves the use of

hold-down bolts
mufflers
reduced speed operation
spring mounts

Answer 10

spring mounts

Question 11

One advantage of rotary compressors over reciprocating compressors is that the

bearings run drier
cavitation is greater
slugging is greater
vibration is less

Answer 11

vibration is less

Question 12

Slugging is the entry of _____ refrigerant into a compressor. Cavitation is the formation and collapse of _____ in a liquid flowing under pressure.

gaseous; solid particles
gaseous; vapor pockets
liquid; solid particles
liquid; vapor pockets

Answer 12

liquid; vapor pockets

Question 13

One purpose of the accumulator on a rotary compressor is to

add moisture to the refrigerant
increase the compressor’s efficiency keep dirt and debris out of the compressor
reduce the flow out of the compressor

Answer 13

keep dirt and debris out of the compressor

Question 14

Helical compressors differ from rotary compressors in that they have

high volumetric efficiency
no valves
no vanes
tolerance for some slugging

Answer 14

no vanes

Question 15

In a scroll compressor, one scroll is stationary and the other ____ Refrigerant enters the scrolls at the ____ and leaves at the center.

orbits; center
orbits; outer edge
rotates; center
rotates; outer edge

Answer 15

orbits; outer edge

Question 16

The amount of compression in a centrifugal compressor depends on the ____ the impeller, which depends in turn on the impeller’s _____ and rate of rotation.

number of blades on; diameter
number of blades on; shape
tip speed of; diameter
tip speed of; shape

Answer 16

tip speed of; diameter

Question 17

In reverse hydrostatic sealing, the flow of ______ across the seal opposes the flow of ____ across the bearing.

• liquid refrigerant; oil
• liquid refrigerant; water
• refrigerant vapor; oil
• refrigerant vapor; water

Answer 17

refrigerant vapor; oil

Question 18

In multistage centrifugal compressors, thrust loads are reduced by

centrifugal force
impeller shrouds
opposing impellers
reducing the speed

Answer 18

opposing impellers

Question 19

The purpose of a purge system on a condenser is to eliminate _____ from the refrigeration system.

acid
air
dirt
heat

Answer 19

air

Question 20

Reducing a compressor’s capacity by closing pre-rotation vanes raises the pressure in the system’s _____

condenser
evaporator
impeller inlet
purge drum

Answer 20

evaporator

Question 21

Which of the following is an important factor to consider when selecting a motor to run a refrigeration compressor?

Current draw
Horsepower rating
Temperature rise
Vibration characteristics

Answer 21

Horsepower rating

Question 22

Which of the following motors can be used in hermetic compressors?

Capacitor-start, induction-run
Repulsion
Synchronous
Wound-rotor induction

Answer 22

Capacitor-start, induction-run

Question 23

You can reverse the direction of a single-phase induction motor by

• reconnecting the running and starting winding in parallel with each other
reconnecting the running and starting winding in series with each other
reversing the connection of both the running and starting windings
reversing the connection of either the starting or running winding

Answer 23

reversing the connection of either the starting or running winding

Question 24

To change a dual-voltage motor to run on 240 V instead of 120 V, you need to

connect the two running windings in parallel
• connect the two running windings in series
• disconnect one running winding
• disconnect one running winding and connect the other one instead

Answer 24

connect the two running windings in series

Question 25

A single-phase motor used in a hermetic compressor has a relay to disconnect the starting winding from the circuit when the motor approaches its running speed One kind of relay operates when the current in the _____ winding falls to a preset value Another kind operates when the voltage across the _____ winding rises to a preset value. • running; running • running; starting • starting; running • starting; starting

Answer 25

running; starting

Question 26

The two basic categories of motor starting devices are automatic and manual contactors and starters three-phase and single-phase voltage and current

Answer 26

contactors and starters

Question 27

A reduced voltage starter limits the current to the motor at startup in order to prevent • compressor damage • motor damage overheating • voltage drops to other equipment

Answer 27

voltage drops to other equipment

Question 28

Overload protection for compressor motors may be provided by an) • external bimetallic disk • manual override switch • mercury thermometer short-cycle controller

Answer 28

external bimetallic disk

Question 29

Crankcase heaters are especially useful on compressors that are subjected to • cold climates • continuous operation • frequent overloading high discharge pressures

Answer 29

cold climates

Question 30

Installing a suction-line accumulator can protect a compressor from damage caused by high evaporator pressure overheating refrigerant vapor slugging

Answer 30

slugging

Question 31

The "first rule" of preventative maintenance for compressors and related components is to establish a schedule for maintaining all equipment on a regular rotation follow the manufacturer's recommended maintenance schedules and procedures have your work inspected and approved by another qualified technician keep all warranty forms at least two years

Answer 31

follow the manufacturer's recommended maintenance schedules and procedure

Question 32

Typical preventative maintenance procedures for compressors and related equipment include adding oil if the level is too low listening for unusual noises tightening all bolts as much as possible using your spare time to check equipment nearby

Answer 32

listening for unusual noises

Question 33

A compressor may overheat because of a(n) hot discharge line low oil level partial vacuum in the crankcase tight shaft seal

Answer 33

low oil level

Question 34

After disassembling a reciprocating compressor and cleaning the parts, you should inspect the parts for evidence of acid in the oil evidence of moisture in the refrigerant excessive wear on bearing surfaces formation of scale

Answer 34

excessive wear on bearing surfaces

Question 35

When pumping down a compressor for service, run the compressor with the valve on the suction line closed, then close the valve on the discharge line and stop the compressor. Repeat this process until the pressure holds at _____ psig - 5 to -10 +5 to +10 -2 to -5 +2 to +5

Answer 35

+2 to +5