CH. 16

Question 1

The ____ is the value at which a device begins operation.

Answer 1

cut-in

Question 2

A control system’s ____ is the set of numbers between and including cut-in and cut-out values.

Answer 2

range

Question 3

In electronic controls, range adjustment is a function of the ____.

Answer 3

processor

Question 4

A system’s ____ is the number of units between the cut-out and cut-in values.

Answer 4

differential

Question 5

A device used to change one form of energy into another form is a ____.

Answer 5

transducer

Question 6

The desired condition in a control system is called the ____.

Answer 6

set point

Question 7

The difference between the desired condition and the present condition is called the ____.

Answer 7

offset

Question 8

The present condition as measured by the sensor in a control system is the ____.

Answer 8

control point

Question 9

Below-atmospheric-pressure elements ____.

Answer 9

contain volatile fluid in a partial vacuum

Question 10

A bimetal coil ____ as the surrounding air gets warmer.

Answer 10

expands

Question 11

Which of the following statements about electronic sensors is true?

They can accurately sense extremely high and low temperatures.
The sensing device is usually a thermistor.
Correct!
All of the above.
They operate at a low voltage.

Answer 11

All of the above.

Question 12

When high head pressure in a hermetic system causes oil and refrigerant breakdown, the presence of moisture or dirt can result in ____ forming.

sludge
carbon
acids
Correct!
All of the above.

Answer 12

All of the above.

Question 13

In a low-pressure motor control, the cut-out and cut-in pressures are set to maintain proper ____.

Answer 13

evaporator temperature

Question 14

Which of the following statements about the terminals of a current relay is not true?

Answer 14

A current relay is wired by connecting an ungrounded wire to the M terminal.

Question 15

Current relays are ____.
All of the above.
typically wired in series with the run windings
usually found on low-torque, single-phase motors
used to close and open the start winding circuit

Answer 15

All of the above.

Question 16

The pickup voltage required to operate a potential relay is generated when a motor reaches around ____ of its normal operating speed.

Answer 16

3/4

Question 17

Contactors with ____ of contacts are used to control three-phase motor operation.

Answer 17

three or four sets

Question 18

After internal motor overload protection opens the motor circuit due to overheating, a technician should ____ to speed up compressor cooling.

Answer 18

use dry ice and forced air

Question 19

A(n) ____ motor control is mounted on the suction side of the compressor to monitor evaporator suction pressure.

Answer 19

low-pressure

Question 20

A ____ fuse blows immediately after the maximum rating of the fuse is exceeded.

Answer 20

fast-acting

Question 21

A ____ fuse will not blow unless an overload condition exists for a certain period of time.

Answer 21

time-delay

Question 22

Any standard relay may be used to replace a lockout relay.

Answer 22

False

Question 23

An above-atmospheric-pressure element is used to control heating units.

Answer 23

False

Question 24

When the pressure inside an above-atmospheric-pressure element increases, it closes an electrical circuit.

Answer 24

True

Question 25

A flat bimetal strip deforms or bends as temperature rises because the copper expands more than the steel.

Answer 25

True

Question 26

Bimetal discs are often used for fast snap-action applications.

Answer 26

True

Question 27

If a thermistor’s resistance increases as temperature increases, the thermistor has a negative temperature coefficient (NTC).

Answer 27

False

Question 28

An oil pressure motor control connected to a compressor’s lubrication system shuts off the compressor if the oil pressure drops to low-side pressure.

Answer 28

True

Question 29

A low-pressure safety control is set to maintain a specific evaporator temperature.

Answer 29

False

Question 30

A low-pressure safety control is set to shut down the compressor in the event of refrigerant loss.

Answer 30

True

Question 31

Three-phase motors may use the same starting relays that single-phase motors use.

Answer 31

False

Question 32

A PTC relay has a low resistance when the motor circuit is first energized, so it is easier for the current to pass through the PTC relay than through the run capacitor.

Answer 32

True

Question 33

After a PTC relay increases its resistance, the motor current seeks the path of least resistance, which is through the run capacitor.

Answer 33

True

Question 34

In order for a PTC relay’s resistance to drop low enough for a motor to start again, it must have enough time to cool down.

Answer 34

True

Question 35

The fuses for a motor in an HVACR system are usually factory-installed within the compressor dome.

Answer 35

False

Question 36

A fast-acting fuse is commonly used on motors with a high starting current.

Answer 36

False

Question 37

A time-delay fuse may allow a motor to be damaged from high current before the time delay is over.

Answer 37

True

Question 38

Current-limiting fuses use temperature-sensitive resistors that close the motor circuit as temperature rises.

Answer 38

False

Question 39

An internal bimetal protection device will open the motor circuit when the temperature reaches 200°F to 250°F (93°C to 121°C).

Answer 39

True

Question 40

External bimetal protection devices only open a motor circuit if the current is too high.

Answer 40

True

Question 41

If the contact points of a thermostatic motor control were to open very slowly, electric arcing could burn the contacts.

Answer 41

True

Question 42

When the thermistor in a PTC relay has high resistance, it acts as a closed switch or contact.

Answer 42

False

Question 43

If a thermistor’s resistance decreases as the temperature increases, the thermistor has a positive temperature coefficient.

Answer 43

False

Question 44

If a thermistor’s resistance increases as temperature increases, it has a positive temperature coefficient.

Answer 44

True

Question 45

A fuse is an automatic switch that opens a circuit if the current draw exceeds a predetermined level and must be manually reset.

Answer 45

False