Book 2 Chapter 24: Refrigeration Cycle Controls

Question 1

Which of the following are the distinct classes of refrigeration controls?
A) Operating or primary controls
B) Actuating or secondary controls
C) Limiting and safety controls
D) All of the above

Answer 1

D) All of the above

Question 2

In the event of a low oil pressure condition, the oil pressure failure switch will:
A) Open the recycle valve to take the load off the compressor
B) Stop the flow of refrigerant to the system
C) Shut down the compressor
D) Sound an audible alarm

Answer 2

C) Shut down the compressor

Question 3

CSA B52 Mechanical Refrigeration Code requires that all refrigeration systems,except listed and approved factory-sealed systems containing less than _________ of Group A1 refrigerant, and operating above atmosphere pressure, shall be equipped with a pressure limiting device.
A) 10kg (22lb)
B) 5kg (11lb)
C) 15kg (33.1lb)
D) 20kg (44.1lb)

Answer 3

A) 10kg (22lb)

Question 4

Oil pressure failure switches are used to:
A) Keep the oil pressure at a level where the oil will not freeze
B) Keep oil from freezing at low pressure
C) Shutdown the compressor when the oil pressure drops below the minimum
D) Separate refrigerant dissolved in the oil from the lubricant
E) Prevent compressor start-up if the oil heater fails

Answer 4

C) Shutdown the compressor when the oil pressure drops below the minimum

Question 5

Which of the following statements about flow switches is false?
A) They can be used to close flow indicator circuits
B) They are used as lockout switches when flow is insufficient
C) They are operated by the force exerted on a flexible vane immersed in the liquid flowing in the line
D) They can only be used to regulate liquid flow, not air flow
E) They are used on chilled water

Answer 5

D) They can only be used regulate liquid flow, not air flow

Question 6

The maximum setting of a pressure limiting device on the high side of a refrigeration system must not exceed what percentage of the high side design pressure?
A) 100%
B) 75%
C) 80%
D) 90%
E) 50%

Answer 6

D) 90%

Question 7

Which of the following actuating control valves is electromagnetically operated?
A) Thermostat valve
B) Evaporator pressure regulating valve
C) Solenoid valve
D) Condenser cooling water regulating valve
E) Fluid expansion regulator valve

Answer 7

C) Solenoid valve

Question 8

The safety control which uses a current transformer with a resistor in the motor circuit is known as the:
A) High oil temperature cutout
B) Motor overload protection
C) Solenoid valve
D) Low oil sump temperature protection
E) High motor temperature cutout

Answer 8

B) Motor overload protection

Question 9

A bimetallic element converts temperature changes to mechanical motion by having metals with different:
A) Coefficients of thermal conductivity
B) Rates of temperature change
C) Temperatures
D) Coefficients of linear expansion
E) Electron velocities

Answer 9

D) Coefficients of linear expansion

Question 10

Operating or primary controls are used to:
A) Regulate the refrigeration system output when the operating limits are reached
B) Control the operation of cooling water
C) Regulate the refrigeration system output when the system limits are exceeded
D) Indirectly control changes in operation
E) Protect the system from operation beyond set limits

Answer 10

A) Regulate the refrigeration system output when the operating limits are reached

Question 11

Expansion valves:
A) Will expand the liquid to the receiver
B) Relieve high pressure in the receiver
C) Are used to change the refrigeration system
D) Regulate the liquid refrigerant flow to the evaporator
E) Isolate the compressor from the condenser

Answer 11

D) Regulate the liquid refrigerant flow to the evaporator

Question 12

Limiting or safety controls are used to:
A) Protect the system from operation beyond set limits
B) Indirectly control changes in operation
C) Regulate the refrigeration system output when the system limits are reached
D) Control the operation of cooling water
E) Regulate the refrigeration system output when the system limits are exceeded

Answer 12

A) Protect the system from operation beyond set limits

Question 13

The operating control which uses a bimetal element is a:
A) Pressure actuated control
B) Solenoid actuated control
C) Fluid expansion actuating control
D) Humidity actuated control
E) Temperature actuated control

Answer 13

E) Temperature actuated control

Question 14

Flow switches are used on chilled water and cooling water lines and air ducts are used as ___________ switches.
A) Safety lockout
B) Evaporator level control
C) Condenser pressure control
D) Over pressure lockout
E) Low temperature lockout

Answer 14

A) Safety lockout

Question 15

The operation of the compressor (starting, stopping, and unloading) may be accomplished by a ________ type of actuated control.
A) Mass
B) Level
C) Density
D) Volume humidity
E) Pressure

Answer 15

E) Pressure

Question 16

The high motor temperature cutout stops the compressor if there is a loss of motor cooling or a motor overload due to malfunction of the:
A) Operating controls
B) Low limit thermostat
C) High oil temperature cutout
D) Condenser cooling water regulating valve
E) High-pressure safety cutout

Answer 16

A) Operating controls

Question 17

The CSA B52 Mechanical Refrigeration Code requires the pressure limiting device to be connected between the:
A) Compressor and the first stop valve in the suction line
B) Compressor and the first stop valve in the discharge line
C) Condenser and the first stop valve in the discharge line
D) Condenser and the first stop valve in the suction line
E) Evaporator and the first stop valve in the discharge line

Answer 17

B) Compressor and the first stop valve in the discharge line

Question 18

The thermostatic refrigeration controller has a differential adjustment that sets the temperature at which the:
A) Condenser cooling water control activates
B) Level in the evaporator control activates
C) Fan starts and stops
D) Expansion valve opens and closes
E) Cut-in and cut-out occurs

Answer 18

E) Cut-in and cut-out occurs

Question 19

The solenoid valve is operated by a/an ______ signal.
A) Pressure
B) Humidity
C) Electrical
D) Temperature
E) Electronic

Answer 19

C) Electrical

Question 20

One of the most important secondary controls in a refrigerating system is the refrigerant flow control used to regulate the amount of liquid flowing into the:
A) Condenser
B) Refrigerated space
C) Receiver
D) Refrigerator
E) Evaporator

Answer 20

E) Evaporator

Question 21

The sensing device of a humidistat may consist of a/an _________ element.
A) Hydroponic
B) Hygroscopic
C) Hydroscopic
D) Pneumatic
E) Hydrophobic

Answer 21

B) Hygroscopic

Question 22

The low oil sump temperature protection device prevents the compressor from starting if the oil temperature falls below a preset value so that:
A) The oil viscosity will be low enough
B) Any refrigerant dissolved in the oil is separated from the lubricant
C) The oil will drain from the evaporator
D) The oil will flow freely
E) The oil will drain from the condenser

Answer 22

B) Any refrigerant dissolved in the oil is separated from the lubricant

Question 23

In the event of a low oil pressure condition, the oil pressure failure switch will:
A) Shutdown the compressor
B) Sound an audible alarm
C) Open the recycle valve to take the load off the compressor
D) Stop the flow of refrigerant to the system
E) Stop the air circulation fan

Answer 23

A) Shutdown the compressor