RACT Unit 24: Review questions/Practice Test

Question 1

Which is not a pressure or force acting on a TXV diaphragm?

a) spring pressure
b) bulb pressure
c) head pressure
d) evaporator pressure

Answer 1

c) head pressure

Question 2

The needle and seat of a TXV are normally made of

a) brass
b) aluminum
c) copper
d) stainless steel

Answer 2

d) stainless steel

Question 3

The TXV tries to maintain a constant ___________ in the evaporator

a) frost line
b) pressure
c) sub cooling
d) superheat

Answer 3

d) superheat

Question 4

Liquid, Vapour, cross liquid, cross vapour are all types of ________

a) pistons
b) cap tube bores
c) AXV bulb charges
d) TXV bulb charges

Answer 4

d) TXV bulb charges

Question 5

The bulb of the TXV is mounted on the

a) evap outlet
b) evap inlet
c) comp outlet
d) comp inlet

Answer 5

a) evaporator outlet

Question 6

When should an externally equalized TXV be used?

a) when there is excessive pressure drop through the evaporator
b) when the system is a low or medium temp application
c) when the system is equipped with a semi hermetic compressor
d) when the txv is used in a low ambient condition on a single circuit evaporator

Answer 6

A) when there is excessive pressure drop through the evaporator

Question 7

An AXV tried to maintain a constant _________ in the evaporator

a) superheat
b) sub-cooling
c) frost line
d) pressure

Answer 7

d) pressure

Question 8

The TXV responds to an increased heat load by;

a) increasing refrigerant flow
b) decreasing refrigerant flow
c) not reacting to changing heat loads
d) keeping refrigerant flow constant

Answer 8

a) increasing refrigerant flow

Question 9

The three factors that determine the capacity of a TXV are: evaporator temperature, liquid temperature entering the valve, and _________

a) pressure drop across the valve
b) number of evaporator circuits
c) length of the sensing bulb transmission line
d) evaporator pressure

Answer 9

a) pressure drop across the valve

Question 10

How does the automatic expansion valve respond to load increase?

a) it closes, decreasing refrigerant flow
b) it opens, decreasing refrigerant flow
c) it opens, increasing the refrigerant flow
d) it closes, increasing the refrigerant flow

Answer 10

a) it closes, decreasing refrigerant flow

Question 11

On a ___________ TXV, the liquid pressure is cancelled out because it acts on equal areas but in opposite directions.

a) cross vapour
b) cross liquid
c) balanced port
d) pressure-limiting

Answer 11

balanced port

Question 12

If a system with a cap tube metering device is properly changed, when it nears the desired box temp it will have a superheat of approximately;

a) 10 to 15F
b) 15 to 20F
c) 8 to 12F
d) 2 to 5F

Answer 12

c) 8 to 12F

Question 13

A capillary tube meeting device controls refrigerant flow by;

a) pressure drop
b) temperature drop
c) using superheat
d) using a stepper motor

Answer 13

a) pressure drop

Question 14

On a PID controller, the difference between the superheat set point of the controller and the actual superheat is called ___________

a) derivative
b) integral
c) proportion
d) offset

Answer 14

d) offset

Question 15

An EEV uses a _____________ to control the valves port, which in turn controls evaporator superheat

a) sensing bulb transmission line
b) stepper motor
c) capillary tube
d) spring

Answer 15

b) stepper motor

Question 16

The __________ is located inside the valve body and moves the needle in and out of the seat in response to system load changes

a) diaphragm
b) sensing bulb
c) external equalizer
d) transmission line

Answer 16

a) diaphragm

Question 17

The ___________ charge bulb is usually limited to applications that have narrow operating ranges or to special functions like de-superheating on the high side of the system

a) cross vapour
b) vapour
c) cross liquid
d) liquid

Answer 17

d) liquid

Question 18

The ___________ on a TXV is used to compensate for pressure drops from the inlet to the outlet of the evaporator

a) internal equalizer
b) needle and seat
c) sensing bulb and transmission line
d) external equalizer

Answer 18

d) external equalizer

Question 19

To prevent an overloaded compressor during a hot pull down on a low temp cooler, a __________expansion valve can be used

a) balanced port
b) cross liquid
c) pressure-limiting
d) cross vapour

Answer 19

c) pressure limiting

Question 20

The two factors that determine how much liquid will pass through a cap tube at any given pressure drop are the _____________

a) type of refrigerant and oil
b) spring and bulb pressure
c) length and diameter
d) evaporator and suction line size

Answer 20

c) length and diameter

Question 21

explain why entering liquid pressure has no effect on the opening force of a balanced-port TXV?

Answer 21

It is cancelled out because it acts in equal areas but in opposite directions

Question 22

What is meant by MOP TXV

Answer 22

Limit the maximum operating pressure the valve allows the evaporator to experience

Question 23

Explain why systems equipped with a TXV OR AXV require a receiver?

Answer 23

To store refrigerant when it is not needed

Question 24

The three pressures that act to open or close a thermostatic expansion valve are _________________ pressure

a) compressor, condenser, evaporator
b) spring, bulb, orifice
c) evaporator, bulb, spring
d) bulb, compressor, evaporator

Answer 24

c) evaporator, bulb, and spring

Question 25

A TXV with a liquid charged bulb is usually limited to ______________

a) higher temp applications
b) applications that have a narrow operating range
c) systems that operate below atmospheric press
d) applications where the ambient air temp stays above freezing

Answer 25

b) applications that have a narrow operating range

Question 26

The spring tension on a TXV is factory set for a predetermined superheat of _______F

a) 6-10
b) 8-12
c) 6-8
d) 12-15

Answer 26

b) 8 to 12F

Question 27

A TXV with a ________ charge bulb, sometimes referred to as a critical charge bulb, is often called a MOP valve

a) vapour
b) cross vapour
c) liquid cross
d) liquid

Answer 27

a) vapour

Question 28

An external-equalized TXVA must always be installed when a refrigerant distributor is used because of the distributors large pressure drop

Answer 28

true

Question 29

The external equalizer line should always be piped to the suction line before the expansion valve sensing bulb?

Answer 29

false

Question 30

Conditions such as large varying head pressures, widely varying evaporator loads, and very low liquid-line temperatures can be controlled by a ________TXV

a) internally equalized
b) MOP

C) pressure-limiting

D) balanced-port

Answer 30

d) balanced port

Question 31

The controls of a ___________ use algorithms, a set of electronic instructions, and a proportional integral derivative (PID) controller

a) AXV
b) crankcase heater
c) thermostatic expansion valve
d) electronic expansion valve

Answer 31

d) electronic expansion valve

Question 32

An automatic expansion valve (AXV) is designed to maintain a constant __________ in the evaporator

a) pressure
b) oil level
c) superheat

Answer 32

a) pressure

Question 33

The ________ does not control superheat, is a fixed bore device with no moving parts and cannot adjust load changes

a) thermostatic expansion valve
b) automatic expansion valve
c) cap tube
d) electronic expansion valve

Answer 33

c) capillary tube