Book 2 Chapter 23: Refrigeration And AC System Controls

Question 1

What does the automatic expansion valve strive to control?
A) Compressor suction pressure
B) Compressor discharge pressure
C) Refrigerant flow
D) Refrigerant system temperature

Answer 1

A) Compressor suction pressure

Question 2

What are the three controlling pressures in a thermostatic expansion valve?
A) Thermal element
B) Spring
C) Evaporator pressure
D) All of the above

Answer 2

D) All of the above

Question 3

What is the purpose of the “weighted valve pin” used with a high-pressure float valve?
A) Control the flow of refrigerant into the evaporator
B) Reduce the amount of line frosting after the float valve
C) Maintain a back pressure in the condenser
D) Control the pressure in the refrigeration system

Answer 3

B) Reduce the amount of line frosting after the float valve

Question 4

Which of the following are methods used to control the speed of a compressor?
A) Variable-speed electric motor
B) Temperature-sensing device controlling the turbine inlet steam flow
C) Hydraulic coupling installed between a constant speed driver and the compressor to vary the speed
D) All of the above

Answer 4

D) All of the above

Question 5

The most widely used refrigerant control that has a thermal power element consisting of a bellows or a diaphragm chamber connected to a temperature sensing bulb by means of a small capillary tube is a/an:
A) High-pressure float-valve
B) Thermostatic expansion valve
C) Low-pressure float-valve
D) Hand operated expansion valve
E) Automatic expansion valve

Answer 5

B) Thermostatic expansion valve

Question 6

Manual or hand operated expansion valves are seldom used in modern refrigeration systems except for occasionally:
A) In the bypass line around the automatic control valve
B) In the compressor oil cooling system
C) To control the temperature of the evaporator
D) To control the temperature of the condenser
E) To control the temperature of the cooling medium

Answer 6

A) In the bypass line around the automatic control valve

Question 7

What will be the effect if an insufficient amount of liquid refrigerant is admitted to the evaporator by a thermostatic expansion valve?
A) The room temperature will decrease closing the expansion valve
B) The expansion valve will freeze in position
C) The heat in the vapour leaving the evaporator causes the pressure in the thermal element to increase, opening the expansion valve
D) The thermal element reaches an equilibrium leaving the expansion valve in the same position
E) Insufficient force will be generated against the diaphragm and spring to open the expansion valve

Answer 7

C) The heat in the vapour leaving the evaporator causes the pressure in the thermal element to increase, opening the expansion valve

Question 8

Which control is used to maintain a constant level of liquid refrigerant in the liquid accumulator of a flooded evaporator?
A) A thermostatic expansion valve
B) A low pressure float-valve
C) A high pressure float-valve
D) An automatic expansion valve
E) A hand operated expansion valve

Answer 8

B) A low pressure float-valve

Question 9

The control which restricts the flow of liquid from the condenser to the evaporator and maintains a pressure difference between the two units by using a pressure drop resulting from resistance between the device’s length and small bore is called a/an:
A) Bypass line
B) High-pressure float valve
C) Low-pressure float valve
D) Capillary tube
E) External float chamber

Answer 9

D) Capillary tube

Question 10

Which of the following are refrigeration metering or flow control devices?
1. Orifice meter
2. Automatic expansion valve
3. Bourdon tube
4. Thermostat
5. Low-pressure float
6. Capillary tube

A) 4,5,6
B) 2,4,6
C) 3,4,5
D) 1,2,3
E) 2,5,6

Answer 10

E) 2,5,6

Question 11

In a system controlled by a high pressure float valve, insufficient liquid will cause which of the following?
A) Liquid being carried over to the compressor with the vapour
B) Starving the evaporator and reducing the capacity of the system
C) Boosting the compressor’s pressure
D) Automatic system shutdown
E) All of the above

Answer 11

B) Starving the evaporator and reducing the capacity of the system

Question 12

The type of operation that stops the compressor when the desired low temperature of the substance to be cooled is reached and starts the compressor up again when the temperature rises to a set level is called:
A) Unloading operation
B) Cylinder bypass operation
C) Continuous operation with reduced output
D) Intermittent operation
E) Variable guid operation

Answer 12

D) Intermittent operation

Question 13

Which of the statements about automatic expansion valves is false?
A) When the compressor stops, the valve automatically shuts off
B) The valve maintains constant pressure in the evaporator during compressor operation regardless of the load
C) The control valve may be used with multiple cooling coils connected to the same compressor
D) The spring force is countered by evaporator pressure acting upward against the diaphragm which closes the valve
E) A spring exerting a downward force on the diaphragm tends to open the valve

Answer 13

C) The control valve may be used with multiple cooling coils connected to the same compressor

Question 14

The thermostatic expansion valve operates on the principle of balancing:
A) The volumetric expansion of a fluid against a return spring and evaporator pressure
B) Condenser pressure against a return spring
C) Evaporator temperature against a return spring
D) Evaporator pressure against a return spring
E) Condenser temperature against a return spring

Answer 14

A) The volumetric expansion of a fluid against a return spring and evaporator pressure

Question 15

Use of evaporator capacity control results in refrigeration system load changes and thus requires simultaneous:
A) Cooling tower flow rate changes
B) Reduction in air conditioning requirements
C) Compressor capacity control
D) Heating system capacity control
E) All of the above

Answer 15

C) Compressor capacity control

Question 16

The thermostatic expansion valve must admit enough liquid to maintain the superheat at the evaporator outlet at _______ to provide for maximum evaporator efficiency.
A) 2ºC to 3ºC (36ºF to 38ºF)
B) 0ºC to 1ºC (32ºF to 34ºF)
C) 8ºC to 9ºC (46ºF to 48ºF)
D) 5ºC to 6ºC (41ºF to 43ºF)
E) 10ºC to 11ºC (50ºF to 52ºF)

Answer 16

D) 5ºC to 6ºC (41ºF to 43ºF)

Question 17

What is the purpose of the “weighted valve pin” used with a high-pressure float valve?
A) Reduce the amount of line frosting after the float valve
B) Control the flow of refrigeration into the condenser
C) Maintain a back pressure in the condenser
D) Control the flow of refrigerant into the evaporator
E) Control the pressure in the refrigeration system

Answer 17

A) Reduce the amount of line frosting after the float valve

Question 18

One of the disadvantages of evaporator capacity control by face damper is that the:
A) Temperature of the space is reduced
B) Refrigerant volume to the space is reduced
C) Temperature of the space is increased
D) Air volume to the space is reduced
E) Refrigerant pressure to the space is reduced

Answer 18

D) Air volume to the space is reduced

Question 19

The flow of liquid refrigerant from the high to the low-pressure side of the system must be controlled to maintain the desired temperature of the:
A) Compressor discharge
B) Condenser
C) Compressor inlet
D) Cooled medium
E) Cooling air

Answer 19

D) Cooled medium

Question 20

The most common application of evaporator capacity control is to use:
A) Adjustable evaporators
B) Sectional receivers
C) Sectional condensers
D) Variable evaporators
E) Sectional evaporators

Answer 20

E) Sectional evaporators

Question 21

The thermal expansion valve works quite satisfactorily provided the pressure drop across the:
A) Evaporator is small
B) Condenser is small
C) Receiver is small
D) Evaporator is large
E) Condenser is large

Answer 21

A) Evaporator is small

Question 22

The low-pressure float valve is a liquid level operated control valve used to maintain a constant level of liquid refrigerant in the:
A) Evaporator
B) Receiver
C) Expansion valve
D) Condenser
E) Compressor

Answer 22

A) Evaporator

Question 23

All of the following methods are used to control the refrigeration compressor outlet except:
A) Suction throttling
B) Intermittent operation
C) Speed control
D) Cylinder Unloaders
E) Capillary tube

Answer 23

E) Capillary tube

Question 24

The bulb of a thermostatic expansion valve is sensitive to the:
A) Pressure changes in the condenser
B) Pressure changes in the evaporator
C) Temperature changes in the evaporator
D) Temperature changes in the receiver
E) Temperature changes in the condenser

Answer 24

C) Temperature changes in the evaporator

Question 25

One of the safety devices on a centrifugal refrigeration compressor that acts preventing the compressor from being started is the _______ switch.
A) Refrigerant level low
B) Evaporator temperature high
C) Refrigerant level high
D) Condenser temperature low
E) Vane closed

Answer 25

E) Vane closed