Refrigeration excellance Flashcards
(74 cards)
1
Q
- In a dry type (direct expansion) evaporator, liquid refrigerant must boil away as close to the end of the coil as possible in order to:
A
A. Operate at high-efficiency
2
Q
- The difference between the temperature of the refrigerant boiling in the evaporator and the temperature at the evaporator outlet is known as
A
A. Evaporator superheat
3
Q
- An expansion device that is stuck open will cause
A
D. A flooded evaporator
4
Q
- When measuring evaporator superheat on a commercial system that has a long suction line, the pressure reading should be taken at the
A
A. Compressor inlet
5
Q
- Superheat measurements are best taken
A
D. With the system operating at design conditions
6
Q
- A technician is checking the superheat on a multi circuit evaporator and finds one of the circuits has a superheat that is higher than the others. This could be caused by
A
D. A blocked distributor
7
Q
- A TXV with an external equalizer is used on
A
A. Evaporators with a high pressure drop
8
Q
- Dry type evaporators operate most efficiently with the superheat setting of approximately
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A. 8°F to 12°F
9
Q
- An evaporator used to chill liquids is operating within normal superheat setting. But the system is not cooling the product properly. Which of the following is most likely the cause?
A
A. Overcharge of refrigerant
10
Q
- What time interval is required between each superheat adjustment?
A
B. About 10 to 15 minutes
11
Q
- A low temperature evaporator used for cooling space or product refrigeration
A
D. Must be defrosted periodically
12
Q
- Some special applications use a flooded evaporator (operated full of refrigerant) in order to maintain the proper level of liquid refrigerant, a ______ type devices used.
A
D. Low side float
13
Q
- A properly functioning condenser will first
A
D. De-superheat, then sub-cool
14
Q
- The effect of an inefficient water cooled condenser will
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A. Act the same as an air cooled condenser
15
Q
- The refrigerant condensing temperature in a water cooled condenser is normally about _____ higher than the leaving water.
A
B. 10°F
16
Q
- The refrigerant and an air cooled condenser will normally contends at approximately _____ higher temperature than the air passing over it.
A
B. 30°F
17
Q
- Workable head pressure during periods of low ambient temperature can be achieved by using
A
D. Fan cycle control
18
Q
- Cooling towers that pass air over water to remove system heat are limited in capacity by
A
A. Outside air wetbulb temperature
19
Q
- Parallel compressors often referred to as a rack system may use
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A. A common suction, but not a common discharge header
20
Q
- The major difference between a cooling tower and an evaporative condenser is
A
D. The refrigerant is indirectly cooled in the cooling tower
21
Q
- Multiple compressors provide
A
C. Capacity control
22
Q
- A dirty evaporator and subsequent low evaporator pressures will cause
A
B. Low compression ratios
23
Q
- The thermostatic expansion valve (TEV) maintains a constant _______ in the evaporator.
A
D. Superheat
24
Q
- What type of ice is made with the commercial icemaker that uses a gear motor and auger?
A
B. Shaved ice
25
25. Some capillary tube systems take advantage of heat exchange by soldering the capillary tube to the suction line. In order to obtain the correct superheat reading, it must be taken
A. After the capillary tube suction line heat exchanger
26
26. A ______ is usually required for ultra low temperature applications.
D. Cascade system
27
27. A hot gas defrost cycle can be initiated by a
A. Timer
28
28. When the defrost cycle is terminated, the evaporator fans will
D. Delay coming on
29
29. An off-cycle defrost method is often used on evaporators operating at a minimum of
C. 35°F
30
30. Excessive frost on the evaporator causes
B. Reduced heat transfer
31
31. Automatic pump down systems are used to prevent
D. Migration of refrigerant to the crankcase during off cycles
32
32. An automatic pumpdown system requires a
A. Liquid line solenoid
33
33. Short cycling in a pumpdown system is most likely caused by a leaking
A. Liquid line solenoid valve
34
34. An evaporator pressure regulator valve (EPR valve) is a mechanical control that
B. Limits pressure setpoint in the evaporator
35
35. The "low ambient control" is used to control
B. Head pressure
36
36. The crankcase heater is used to prevent
A. Refrigerant migration to the compressor crankcase during the off cycle
37
37. The type of compressor that allows access to the internal components is the
C. Semi hermetic
38
38. Low ambient temperatures seriously affect
A. Water cooled units
39
39. Water cooling towers require a periodic blow down to control
D. Scaling
40
40. High temperature refrigeration applications normally provide box temperatures of
A. 47°F to 60°F
41
41. Medium temperature refrigeration applications will normally provide box temperatures of
D. 30°F to 42°F
42
42. Low temperature refrigeration applications, other than ice makers, will normally provide box temperatures of
A. 0°F to 32°F
43
43. What is the purpose of an oil separator?
A. To capture oil and prevent it from traveling throughout the system
44
44. Blended refrigerants should be charged into a running system
B. As a liquid through a throttling valve into the low side
45
45. A refrigeration system that uses the evaporator of the first stage to exchange heat with the condenser of the second stage refrigeration system is called a
B. Cascade system
46
46. To achieve peak efficiency and performance in a capillary tube system,
D. The system must be critically charged
47
47. Expendable refrigerant means
D. It can be used one time
48
48. If a walk-in cooler requires a high percentage of moisture in the air due to the product being stored, the logical evaporator TD would be
B. 20°F
49
49. "Pump down" means to capture system refrigerant in the
C. Condenser and/or liquid receiver
50
50. What is the normal operating position for a compressor service valve?
B. Back seated
51
51. The suction accumulator prevents flood back from which of the following?
C. Flooding after hot gas termination
52
52. When the compressor service valve is back seated, which port is closed?
C. Service port
53
53. When work on a refrigerator is complete, the compressor service valves should be in what position?
A. Back seated
54
54. What type of oil is used with HFC refrigerant?
A. Alkyl-benzene
55
55. On an expansion valve refrigeration system, a low pressure control can indirectly be used for
D. Controlling box temperature
56
56. What valve is used to connect multiple evaporators of different temperatures to a single compressor?
B. Evaporator pressure regulator (EPR)
57
57. What valve is used to prevent evaporator pressure from falling below a set limit?
B. Evaporator pressure regulator (EPR)
58
58. What valve is used to control excessive pressure entering the compressor during a hot pull down?
C. Crank case pressure regulator (CPR)
59
59. The oil return orifice inside a suction line accumulator is designed to
C. Meter liquid refrigerant and oil at acceptable rate
60
60. Why do suction line filter dryer's have two service ports?
B. To enable checking pressure drop across the dryer
61
61. A thermostatic expansion valve (TXV) that creates an unstable suction pressure is said to be
C. Hunting
62
62. Head pressure control valves permit hot gas to travel directly to the
B. Evaporator
63
63. Liquid slugging of the compressor can be caused by
B. TXV hunting
64
64. A severe evaporator freeze up may cause
C. Liquid flood back
65
65. The oil separator is installed in the
B. Discharge line
66
66. If an oil separator is not used,
A. Oil traps should be installed in all vapor carrying lines
67
68. The relationship between low side absolute pressure and high side absolute pressure is called
C. Compression ratio
67
67. If a system has a long suction line riser, an oil trap should be installed
D. Every 15 to 20 feet of vertical rise
68
69. Capacity control of a large compressor can be performed with
C. Unloaders
69
70. Vibration eliminator's should be installed _______ to the compressor crankshaft centerline.
A. Perpendicular
70
71. What pH level is considered neutral and desired for ice machine or cooling tower applications?
B. 7
71
72. On a rack of multiple compressors, each compressor is controlled by
D. CPR valve
72
73. Which refrigerant line is most sensitive to improper sizing?
A. Liquid line
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