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HVAC 1030 & 1040 > Test 1040 > Flashcards

Test 1040 Flashcards

1
Q

What does the term three phase refer to on three phase motors?

A

A system consisting of three alternating currents of the same frequency, which are offset in phase by 120 degrees.

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2
Q

Three phase motor will have the same resistance reading on across each winding. True or false?

A

True

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3
Q

Three phase motors require the assistance from capacitors. True or false?

A

False

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4
Q

What do we call it once a three-phase motor loses one voltage leg?

A

Single phasing

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5
Q

If air flow is restricted on a direct drive blower, what happens to the motor operating amperage?

A

It increases

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6
Q

How do you tell if a winding is short when using an ohmmeter on a motor?

A

Resistance reading is very low or zero

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7
Q

How do you tell if a winding is open when using an ohmmeter on a motor?

A

Resistance reading is infinity

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8
Q

How do you tell if a winding is ground when using an ohmmeter on a motor?

A

Resistance reading is low between winding and ground (0 ohms)

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9
Q

How do you tell if a winding is good when using an ohmmeter on a motor?

A

Resistance reading is within specified range

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10
Q

Checking a compressor single phase motor winding from common to start and getting an infinity reading means what?

A

The start winding is open

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11
Q

At what percentage of total RPMs is the capacitor taken out of the circuit in a motor using a centrifugal switch?

A

Approximately 75% to 80%

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12
Q

What is a symptom of an open start capacitor on a capacitor start motor?

A

The motor fails to start

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13
Q

Which motor winding has the highest resistance?

A

The start winding

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14
Q

What determines the RPMs of a motor?

A

The frequency of the power supply and the number of poles in the motor

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15
Q

If a capacitor produces 15 amps with a 230-volt AC power supply, what would the microfarad rating be?

A

Approximately 66 microfarads

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16
Q

Are the contacts of the potential relay normally open or normally closed?

A

Normally open

17
Q

The coil of a potential relay is made up of many turns of wire and operates off what?

A

Current sensing
(Electromotive force)

18
Q

What would be the best instrument to test water-soaked windings?

A

Insulation resistance tester

19
Q

When reading motor winding resistance, what are we setting our meter to read?

A

Ohms

20
Q

How do we reverse the rotation of a three-phase motor?

A

By swapping any two of the three phase connections

21
Q

How do you identify the common, start, and run terminals in a motor?

A

Refer to the motor wiring diagram

1-2 has highest resistance then 2 is start
1 and 2 must be start and run
Remaining 3 must be common

1-3 yield lowest resistance which means 3 is common. 1 must be run bc lowest reading should be common to run and remaining terminal is start

22
Q

A belt driven blower’s airflow will increase when the drive pulley diameter is increased or decreased?

A

Decreased

23
Q

What is the max voltage imbalance we can have on a three-phase motor before service is required?

A

10%

24
Q

Reading infinity on an ohmmeter when checking resistance means what?

A

There is an open circuit

25
Q

What condition is the biggest safety hazard for the customer and technician when working on faulty condition? Short, open or ground?

A

Ground

26
Q

On a split phase motor with a centrifugal switch is at rest, what condition is the switch in?

A

Closed

27
Q

On a capacitor start motor with a centrifugal switch is at rest, what condition is the switch in?

A

Closed

28
Q

What type of capacitor is encased in plastic?

A

Start capacitor

29
Q

How would a faulty capacitor affect the operation of a motor?

A

It may cause the motor to fail to start or run inefficiently

30
Q

1 phase, no capacitor, low starting torque, elect. Run, mag start

A

Shaded pole

31
Q

1 phase, no capacitor, low torque, elect run, elect start

A

Split phase

32
Q

1 phase, start cap, med torque, elect run, elect start

A

Capacitor start induction run

33
Q

1 phase, run cap, med torque, elect run, elect start

A

Permanent split capacitor

34
Q

1 phase, start cap, run cap, high torque, elect run, elect start

A

Capacitor start capacitor run

35
Q

3 phase, high torque, N poles per phase

A

3 phase

HVAC 1030 & 1040 (9 decks)

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