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CMC Test Preperation > Modern Refrigeration and AC > Flashcards

Modern Refrigeration and AC Flashcards

0
Q

When liquid refrigerant enters the evaporator, the refrigerant is suddenly at a (High Temp and High Press, Low Temp and High Press, Low Temp and High Press or High Temp and Low Press)?

A

At a low pressure and a high temp

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1
Q

What is used to control the capacity of a commercial compressor?

A

Unloaders

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2
Q

All of the following effect the capacity of a TXV (thermostatic expansion valve) except an ____________ ________________.

A

An external equalizer

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3
Q

What system uses a silicone carbide igniter?

A

Hot surface

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4
Q

What is the process of expanding or enlarging a copper tube to receive another copper tube?

A

Swaging

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5
Q

All are true of a muffler except…

A

Can be installed only on intake of compressor

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6
Q

What device prevents slugging in a heat pump system?

A

Accumulator

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7
Q

Type of circuit where components are arranged in ladder like arrangement?

A

Parallel circuit

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8
Q

A starter relay drops which of the following out of the circuit?

A

Start windings

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9
Q

Thermal device that opens its contacts when motor heater coil uses too much voltage is called a _____________ _________.

A

Thermal relay

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10
Q

How do cooling towers cool?

A

By evaporation

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11
Q

What color is a dot in a moisture site gage system when indicating a dry system?

A

Green

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12
Q

A suction line riser should have a trap installed at the lowest point to….

A

provide reservoir for oil that drips down riser

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13
Q

A yellow tip flame indicates a lack of primary ______ when burning fuel gases in a furnace

A

primary air

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14
Q

What determines defrost termination on a heat pump system using time initiated, temperature terminated defrost cycle?

A

Outdoor coil

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15
Q

What does white smoke from an oil burner indicate?

A

Lein oil and air mixture

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16
Q

Highest temperature at which substance may be liquefied regardless of pressure?

A

Critical temperature

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17
Q

What rating measures furnace efficiency?

A

AFUE

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18
Q

What is the purpose of a condenser?

A

Cools refrigerant to desired temperature

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19
Q

From the expansion valve, the external equalizer runs to…

A

The outlet of the evaporator

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20
Q

Raising superheat will ____________ an evaporator?

A

Starve

21
Q

A device without moving parts that converts ac voltage to a different voltage is called a _________________.

A

Transformer

22
Q

Control for refrigeration unit is set to cut in at 45 degrees and out at 35 degrees. If the setting is changed to 45 degrees cut in and 36 degrees cut out, the compressor will have to… (Run less and cycle more or OR run more and cycle less?)

A

Run less and cycle more

23
Q

A tech finds discharge pressure on a fully charged system is low due to low ambient temperature. How do you resolve this?

A

Install low ambient fan control

24
Q

The pressure in a system is 32.5 PSIA, what is the gauge pressure? (17.8, 32.5, 47.2 or 61.9)

A

17.8

25
Q

A manual switch bears markings “1” and “0”. What does this indicate?

A

On/Off

26
Q

What is a type of condensing temperature control?

A

Fan cycling switch

27
Q

Oil from a hermetic compressor is tested and found to contain acid. This means the compressor has ________________ motor windings.

A

deteriorating motor windings

28
Q

What controls refrigerant migration in a single compressor, multiple evaporator system?

A

Check valve

29
Q

What is the unit of current or rate of flow of electricity?

A

Amps

30
Q

Instrument used to measure relative humidity by comparing wet bulb to dry bulb is called a…

A

Psychrometer

31
Q

What is required when multiple A/C condensing units are installed outside and evaporators are installed at a different location in building.

A

Evaporators must be marked and individually identified

32
Q

If required, a refrigerant relief vent is usually located at the ________ ______________.

A

liquid receiver

33
Q

Pressure gauge of r22 system reads 248 psig and actual line temperature is 100 degrees. What is the amount of subcooling? (12, 14, 16, 18 degrees)

A

16 degrees

34
Q

What component of a high efficiency gas furnace is not found on a mid-efficiency furnace?

A

Secondary heat exchanger

35
Q

What kind of circuit has infinite resistance and no current? (Open, Closed, Shorted, Grounded)

A

Open

36
Q

How many BTU is required to heat 20 lbs of water from 45 degrees to 85 degrees?

A

800 BTUs

page 45

37
Q

The low side of a refrigeration system is characterized by (Evaporator, Suction line, Accumulator)

A

Suction Line

Page 132

38
Q

Condensers remove heat from the refrigerant that it picked up in the evaporator. True or False

A

True

39
Q

What controls an automatic expansion valve?

A

Evaporator pressure

40
Q

What is the purpose of an evaporator pressure regulator?

A

To keep the evaporator pressure above a predetermined point.

41
Q

The capacity of a TEV varies according to all of the following except which of the following: (orifice, pressure differential between high and low side, temperature and condition of the refrigerant in the liquid line, external equalizer)

A

External equalizer

42
Q

What electrical device converts alternating current to direct current?

A

Rectifier

43
Q

How do you measure alternating current of a circuit with a meter?

A

Connect the meter in series

44
Q

What is the latent heat load in BTU/h of air at 1,500 CFM and the absolute humidity difference is 28 grams?

A

28,560 BTU/h

Formula is (0.68 x cfm x grains per pound of dry air)

45
Q

Sensible heat is a measurement of ____ bulb.

A

dry bulb

46
Q

What is the possible cause of a yellow flame?

A

Lack of primary air

47
Q

Where is the oil pressure safety cutout located?

A

Connected to the oil pump at low pressure side

48
Q

In an HVACr system’s refrigerant drier, a substance that collects and holds moisture is called a ___________. In dehumidification, a hygroscopic substance that absorbs moisture from the air.

A

Dessicant

49
Q

The transfer of heat from one place to another by means of a liquid to a gas is __________.

A

Convection

50
Q

The flow of heat between substances by molecular vibration is called ________________.

A

Conduction

51
Q

The specific heat capacity for air is ___._____ BTU/Lb F

A

0.24 BTU/Lb F

CMC Test Preperation (10 decks)

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