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Flashcards in RACT unit 23 Review questions Deck (20)
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1

Which of the following best describes the function of a compressor?

a) the compressor restricts the flow of ref. that enters the evaporator

b) the compressor pumps liquid refrigerant into the condenser to transfer heat

c) the compressor is used to throttle a thermostatic expansion valve (TXV) open or closed

d) the compressor increases the pressure in the system from the low side pressure to the high side pressure

d) the compressor increases the pressure in the system from the low side pressure to the high side pressure

2

Five types of compressors are:

reciprocating

rotary

scroll

screw

centrifugal

3

Which of the following is true of HVACR compressors?

a) a compressor cannot compress liquid

b) a compressor can compress a liquid

c) a compressor requires liquid refrigerant for lubrication

a) a compressor cannot compress a liquid

4

What would be considered a higher than normal temperature of a discharge gas line on a reciprocating compressor?

a) 190F
b) 200F
c) 250F
d) 175F

c) 250F

5

Which compressor type uses pistons to compress the gas?

reciprocating

6

Which compressor type uses tapered, machined gear components to trap the gas for compressors?

a) scroll
b) reciprocating
c) rotary
d) screw

screw

7

What style of compressor uses belts to turn the compressor?

a) open drive
b) closed drive
c) chassis drive
d) hermetic drive

a) open drive

8

What would be done to increase the compressor speed on a belt-driven compressor?

a) decrease drive pulley size
b) increase drive pulley size
c) increase driven pulley size
d) both A and C

a) decrease drive pulley size

9

Which do the following design factors can affect the efficiency of a reciprocating compressor?

a) the two tapered, machined, screw type gears

b) the connecting rod and muffler

c) the piston and the internal springs

d) the valve plate design and clearance volume

d) the valve plate design and clearance volume

10

A medium temperature R-134A system that has a suction pressure of 22psig and discharge pressure of 185psig would have a compression ratio of:

185 + 14.7 = 199.7psia discharge
22 + 14.7 = 36.7psia suction


199.7/36.7 = 5.44:1

11

A direct drive compressor typically runs at _____rpm or _____rpm

1750rpm or 3450rpm

12

A piston, connecting rod, crankshaft, valves, valve plate are parts that may be found in a __________ compressor

reciprocating

13

What effect does a slight amount amount of liquid refrigerant have on a compressor over a long period of time?

it dilutes the oil and causes wear on any moving parts (liquid slugging)

14

What lubricates the refrigeration compressor?

a) refrigerant
b) moisture
c) desiccants
d) oil

d) oil

15

What can the service technician do to keep the refrigeration system operating at peak efficiency?

a) recover refrigerant charge and replace annually

b) replace compressor oil every 3 years or 3000hrs

c) replace crankshaft and connecting rods

d) clean the evap and cond coils to keep pressures within design parameters

d) clean evaporator and condenser coils to keep pressures within design parameters

16

A __________ compressor is usually considered to be a low side device because the suction gas is vented to the inside of the shell, including the crankcase

hermetic

17

State the main advantage that a discuss compressors valve plate design has over a conventional piston type compressors?

discuss valve allows closer tolerance inside the compressor cylinder at the top dead-centre

18

Briefly describe how the scroll compressor compresses a refrigerant gas?

One scroll is fixed and one is vibrating against it creating pockets for compression

19

list four main advantages a scroll compressor has over a conventional piston-type compressor?

- Allows for some liquid

- No valve noise and very soft vibration

- No volumetric losses through gas re-expansion

- mating scrolls maintain nearly continuous compression and leak free contact

20

What are two main reasons why a compressor should have a modulating capacity control?

- Reduces power consumption

- produces better humidification controls

- small compressor starting currents