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RACM > REF UNIT 25 > Flashcards

REF UNIT 25 Flashcards

1
Q

(25.2) What does an EPR do?

A

keeps refrigerant pressure in evaporator from going below a predetermined point

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2
Q

(25.2) What is the opening pressure and what is the closing pressure in an EPR?

A

the evaporator pressure is the opening force, and the spring pressure is the closing force. the evaporator outlet pressure cancels itself out.

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3
Q

(25.2) what are EPR valves AKA?

A

ORI (OPEN on RISE of INLET) or holdback valve

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4
Q

(25.2) on a multiple evaporator system, which evaporator does not need an EPR

A

the one with the lowest SST

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5
Q

(25.2) how do EEPR valves work?

A

they use a stepper motor that responds to microprocessor that responds to box temp

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6
Q

(25.3) what do CPR (crankcase pressure regulating) valves do?

A

limits pressure to compressor in suction line. Keeps compressor from overloading.

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7
Q

(25.3) What type of valve is a CPR?

A

CRO (CLOSE on RISE of OUTLET)

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8
Q

(25.3) When should the CPR be adjusted?

A

during hot pulldown

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9
Q

(23.3) T or F: Oil separators have a float inside that let’s oil out when it rises.

A

true

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10
Q

(25.3) what is the purpose of the crankcase heater?

A

protects the compressor from refrigerant migration. it heats during off cycle.

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11
Q

(25.3) oil pumps are usually used in what capacity compressors?

A

over 3 HP

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12
Q

(25.3) what are the two types of oil pumps?

A

gear type or eccentric type

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13
Q

(25.3) How do eccentric oil pumps work?

A

it squeezes the oil though small holes

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14
Q

(25.4) what are the 4 most common methods of keeping head pressures up in low ambient conditions?

A

fan cycling, fan speed control, shutters, condenser flooding

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15
Q

(25.4) what does condenser splitting do?

A

both condensers used in summer, one used in winter

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16
Q

(25.4) why is a high-pressure control more necessary on water-cooled compressors than air-cooled condensers?

A

because an interruption of water is more likely than an interruption of air.

17
Q

(25.4) what is low-ambient fan control?

A

stops condenser fan in response to low head pressure.

18
Q

(25.4) how does an oil pressure control work?

A

it works on a pressure differential, ensuring there is positive oil pressure in the crankcase, usually about 20psi

19
Q

(25.4() T or F: the oil pressure control uses a time delay so that the compressor has time to build oil pressure

A

true

20
Q

(25.4) what is used so that the oil pressure control doesn’t open if an internal motor protection device opens?

A

a current-sensing relay

21
Q

(25.4) what are pilot-operated solenoid valves?

A

solenoids that mostly use difference in pressure so that it isn’t a massive load to operate

22
Q

(25.4) how does an automatic pump down system work?

A

closes a liquid line solenoid valve when de-energized

23
Q

(25.7) what is the first on the evaporator called?

A

hoar frost

24
Q

T or F: the colder the evaporator, the more fins it needs

A

false. it’s the opposite.

25
Q

(25.7) what is off-cycle defrost?

A

using the air in the box to defrost the coil in off-cycle

26
Q

(25.7) what is random defrost?

A

defrost that is done when the system has the capacity to perform a defrost cycle.

27
Q

(25.7) T or F: defrost on low-temp evaporators are always planned.

A

true

28
Q

(25.7) why is it important for the evaporator fan to be off during defrost?

A

so that the fan doesn’t blow the dripping moisture all up in the place.

29
Q

(25.7) what is the fail-safe?

A

when the timer on the time lock runs a certain amount of time during defrost if the coil isn’t sensed to be above freezing so that electric heaters don’t cause damage.

30
Q

(25.3) why should oil separators be kept warm?

A

so that liquid refrigerant doesn’t condense and then re-enter the crankcase on start up.

RACM (23 decks)

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