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UA Star Exam > TEST PREP > Flashcards

TEST PREP Flashcards

1
Q
  1. CAVITATION CAN DESTROY A CENTRIFUGAL PUMP, IS NOISY AND IS CAUSED BY:
A

INLET PRESSURE THAT IS TOO LOW.

Inlet pressure that falls below the manufacturer’s recommended Net Positive Suction Head (NPSH) will cause water to boil due to the low pressure, causing bubbles and cavitation.

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2
Q
  1. A VACUUM BREAKER IS INSTALLED BETWEEN EQUIPMENT AND A STEAM TRAP TO:
A

ALLOW CONDENSATE TO DRAIN AFTER THE STEAM HAS BEEN SHUT OFF.

Once steam supply has been shut off, steam will condense and will be unable to drain because of the vacuum. The vacuum breaker provides a vent and allows the condensate to drain.

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3
Q
  1. TWO TYPES OF THERMAL OVERLOAD RELAYS IN COMMON USE TODAY ARE:
A

THE BIMETAL RELAY AND THE MELTING ALLOY RELAY.

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4
Q
  1. THE EFFICIENCY OF AN ELECTRIC FURNACE IS USUALLY:
A

100 %

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5
Q
  1. DEFECTIVE RIGGING COMPONENTS AND HARDWARE SHOULD BE:
A

DESTROYED

Inspection for damage of sling and all fastenings and attachments should be made PRIOR TO EACH SHIFT.

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6
Q
  1. IN ORDER TO REDUCE PRESSURE TO AN ACETYLENE PRESSURE REGULATOR, THE ADJUSTING SCREW IS TURNED:
A

COUNTER-CLOCKWISE UNTIL THE TENSION IS OFF.

Pressure adjusting screw. The regulator adjusting screw controls the flow of gas and delivery pressure to the hose and torch.

Soldering & Brazing
Ch. 6 Pg. 90

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7
Q
  1. SUCTION GAS TEMPERATURE LEAVING EVAPORATOR MINUS SATURATED SUCTION TEMPERATURE EQUALS:
A

SUPERHEAT

HVACR Training Manual
Unit 3.11 Page 39

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8
Q
  1. WHICH OF THE FOLLOWING GASES MUST NEVER BE USED TO PRESSURIZE OR LEAK TEST A REFRIGERATION SYSTEM:
A

OXYGEN

Precautions:

  1. Nitrogen must be oil-pumped dry nitrogen.
  2. Although (CO2) Carbon Dioxide could be used, NEVER use just oxygen or just acetylene.
  3. When using high-pressure gas such as n nitrogen or carbon-dioxide in cylinders, always use a pressure regulator and a relief valve.
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9
Q
  1. FOR ELECTRIC HEAT FURNACE WHAT SIZE SHOULD THE FLUE PIPE BE:
A

NO FLUE IS REQUIRED

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10
Q
  1. A REFRIGERANT HEAT EXCHANGER MIGHT CAUSE:
A

THE COMPRESSOR TO BE OVERHEATED

Precautions:

  1. Must be constructed and installed so as to not trap oil.
  2. The amount of superheating should be limited, as excessive superheating of suction gas will cause excessive discharge temperature and overheat the compressor.
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11
Q
  1. THE PURPOSE OF A SUCTION LINE ACCUMULATOR IS TO:
A

TRAP LIQUID REFRIGERANT

Installed in the suction line between the evaporator and the compressor. Basically a tank; a slug of liquid refrigerant and/or oil leaving the evaporator will be trapped in the accumulator.

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12
Q
  1. THE PROPER LOCATION FOR AN OIL SEPARATOR IS NEAR THE:
A

COMPRESSOR

An oil separator is a tank-like device which removes oil from the refrigerant and automatically returns the oil to the compressor.

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13
Q
  1. THE TWO PLANES OF ALIGNMENT THAT MUST BE CONSIDERED WHEN ALIGNED A FLEXIBLE COUPLING ARE:
A

PARALLEL AND ANGULAR

Shafts must be aligned so that the centerlines meet each other exactly in the center (parallel to one another, or axially) and they must be aligned so that they have no angular difference between them (also called radical alignment).

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14
Q
  1. HOW CAN YOU IDENTIFY REVERSE OPERATION WITH A SCROLL COMPRESSOR?
A

BOTH:
. THE COMPRESSOR WILL NOT COMPRESS
. THE COMPRESSOR WILL STOP ON MOTOR OVERLOAD

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15
Q
  1. WHAT SHOULD YOU INSTALL AT THE BOTTOM OF A SUCTION LINE RISER?
A

A P-TRAP

Getting oil to flow upward in certain vertical piping can be a problem, and a trap at the bottom of the riser can assist in getting the oil to begin the upward flow. Also prevents oil in certain lines from draining back to the compressor during the off-cycle.

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16
Q
  1. CONDENSER SATURATION TEMPERATURE ON AIR COOLED CONDENSER SHOULD BE HIGHER THAN THE AMBIENT TEMPERATURE BY:
A

30 DEGREES F TO 35 DEGREES F

. The refrigerant inside the coil of an Air-Cooled Condenser will normally condense at 30 degrees F higher than the air passing over it (also known as ambient air).
. With the outside air temperature of 95 degrees F, the condensing temperature will be about 125 degrees F.

17
Q
  1. THE COMPRESSION RATIO IN A SYSTEM CAN BE DETERMINED BY:
A

DIVING DISCHARGE PRESSURE ABSOLUTE BY SUCTION PRESSURE ABSOLUTE

Compression Ration = Discharge Pressure, psia / Suction Pressure, psia

18
Q
  1. What is the “Rule of Thumb” in BTU’s per hour of heat rejection of a condenser?
A

15,000

Heat rejection of an A/C system is about 15,000 Btu per hour for every 12,000 Btu per hour of cooling capacity, or 15,000 divided by 12,000 equals 1.25 times the net refrigeration effect.

19
Q
  1. The three pressures that operate the Thermal Expansion Valve are Bulb, Spring, and Evaporator.
A

Bulb opens, Spring closes, evaporator closes the valve

. Bulb pressure works through the capillary tube on the top of the valve diaphragm and it acts to open the expansion valve.
. The evaporator pressure works under the diaphragm in the direction in the direction of closing the valve. This pressure is equal to the pressure which corresponds with the refrigerant saturation temperature.
. Spring pressure also acts to close the expansion valve. This pressure is transmitted through the top of the pin carrier the push rods to the underside of the diaphragm.

20
Q
  1. How many BTU’s are there in 8 kW of electrical power?
A

27,304 Btu’s

. The unit of measurement for electrical power is the watt (W).
. a kilowatt = 1000 watts
. 1 kW = 3413 Btu

21
Q
  1. An enthalpy controlled economizer system uses _____________
    for change from mechanical cooling to economizer operation:
A

Outside temperature and humidity sensor.

. An enthalpy sensor reacts to the total heat content of air, both sensible and latent energy.

22
Q
  1. For a voltage measurement the meter is connected:
A

In parallel with the load

. Used to measure voltage drop, or a potential difference, across any part of a circuit

23
Q
  1. If the voltage is kept constant at 240 volts, and the resistance measures 40 ohms, the current flowing through the conductor is:
A

6 amps

. R = I / E
. E = I x R
. I = E / R

24
Q
  1. VA is the common term for:
A

Watts

. Electrical power relates to the time rate of doing work
. The definition of electrical wattage is 1 watt of power is used to perform work when 1 volt causes 1 ampere of current flow for 1 second.
. VA = Volts x Amps

25
Q
  1. The device which operates similar to a fuse, but which can be reused, is a:
A

Circuit Breaker

Fuses and Circuit Breakers are the two MAJOR types of circuit protectors.
. A fuse is used in a circuit to protect the wiring against overloads.

26
Q
  1. Fuses are sized by the ________ they can carry.
A

Amperage and Current

. Sized according to the amount of amperage they will carry without breaking the circuit.
. When excessive current flows through the circuit, the fuse begins to heat up. When that temperature reaches the melting point, the conductor melts (blows), breaking the circuit.

UA Star Exam (1 decks)

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