Refrigeration Cycle Controls

Question 1

Oil pressure failure switches are used to:

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

Answer 1

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

Question 2

Which of the following statements about flow switches is false?

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

Answer 2

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

Question 3

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) 80%
C) 75%
D) 50%
E) 90%

Answer 3

E) 90%

Question 4

Which of the following actuating control valves is electromagnetically operated?

A) Condenser cooling water regulating valve
B) Fluid expansion regulator valve
C) Thermostat valve
D) Evaporator pressure regulating valve
E) Solenoid valve

Answer 4

E) Solenoid valve

Question 5

The safety control which uses a current transformer with a resistor in the motor circuit is known as the:

A) Solenoid valve
B) High oil temperature cutout
C) Low oil sump temperature protection
D) Motor overload protection
E) High motor temperature cutout

Answer 5

D) Motor overload protection

Question 6

A bimetallic element converts temperature changes to mechanical motion by having metals with different:

A) Temperatures
B) Rates of temperature change
C) Coefficients of linear expansion
D) Electron velocities
E) Coefficients of thermal conductivity

Answer 6

C) Coefficients of linear expansion

Question 7

Operating or primary controls are used to:

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

Answer 7

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

Question 8

Expansion valves:

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

Answer 8

B) Regulate the liquid refrigerant flow to the evaporator

Question 9

Limiting or safety controls are used to:

A) Regulate the refrigeration system output when the system 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 9

E) Protect the system from operation beyond set limits

Question 10

The operating control which uses a bimetal element is a:

A) Humidity actuated control
B) Pressure actuated control
C) Solenoid actuated control
D) Fluid expansion actuating control
E) Temperature actuated control

Answer 10

E) Temperature actuated control