Refrigeration excellance Flashcards
- 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. Operate at high-efficiency
- The difference between the temperature of the refrigerant boiling in the evaporator and the temperature at the evaporator outlet is known as
A. Evaporator superheat
- An expansion device that is stuck open will cause
D. A flooded evaporator
- When measuring evaporator superheat on a commercial system that has a long suction line, the pressure reading should be taken at the
A. Compressor inlet
- Superheat measurements are best taken
D. With the system operating at design conditions
- 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
D. A blocked distributor
- A TXV with an external equalizer is used on
A. Evaporators with a high pressure drop
- Dry type evaporators operate most efficiently with the superheat setting of approximately
A. 8°F to 12°F
- 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. Overcharge of refrigerant
- What time interval is required between each superheat adjustment?
B. About 10 to 15 minutes
- A low temperature evaporator used for cooling space or product refrigeration
D. Must be defrosted periodically
- 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.
D. Low side float
- A properly functioning condenser will first
D. De-superheat, then sub-cool
- The effect of an inefficient water cooled condenser will
A. Act the same as an air cooled condenser
- The refrigerant condensing temperature in a water cooled condenser is normally about _____ higher than the leaving water.
B. 10°F
- The refrigerant and an air cooled condenser will normally contends at approximately _____ higher temperature than the air passing over it.
B. 30°F
- Workable head pressure during periods of low ambient temperature can be achieved by using
D. Fan cycle control
- Cooling towers that pass air over water to remove system heat are limited in capacity by
A. Outside air wetbulb temperature
- Parallel compressors often referred to as a rack system may use
A. A common suction, but not a common discharge header
- The major difference between a cooling tower and an evaporative condenser is
D. The refrigerant is indirectly cooled in the cooling tower
- Multiple compressors provide
C. Capacity control
- A dirty evaporator and subsequent low evaporator pressures will cause
B. Low compression ratios
- The thermostatic expansion valve (TEV) maintains a constant _______ in the evaporator.
D. Superheat
- What type of ice is made with the commercial icemaker that uses a gear motor and auger?
B. Shaved ice
- 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
- A ______ is usually required for ultra low temperature applications.
D. Cascade system
- A hot gas defrost cycle can be initiated by a
A. Timer
- When the defrost cycle is terminated, the evaporator fans will
D. Delay coming on
- An off-cycle defrost method is often used on evaporators operating at a minimum of
C. 35°F
- Excessive frost on the evaporator causes
B. Reduced heat transfer
- Automatic pump down systems are used to prevent
D. Migration of refrigerant to the crankcase during off cycles
- An automatic pumpdown system requires a
A. Liquid line solenoid
- Short cycling in a pumpdown system is most likely caused by a leaking
A. Liquid line solenoid valve
- An evaporator pressure regulator valve (EPR valve) is a mechanical control that
B. Limits pressure setpoint in the evaporator
- The “low ambient control” is used to control
B. Head pressure
- The crankcase heater is used to prevent
A. Refrigerant migration to the compressor crankcase during the off cycle
- The type of compressor that allows access to the internal components is the
C. Semi hermetic
- Low ambient temperatures seriously affect
A. Water cooled units
- Water cooling towers require a periodic blow down to control
D. Scaling
- High temperature refrigeration applications normally provide box temperatures of
A. 47°F to 60°F
- Medium temperature refrigeration applications will normally provide box temperatures of
D. 30°F to 42°F
- Low temperature refrigeration applications, other than ice makers, will normally provide box temperatures of
A. 0°F to 32°F
- What is the purpose of an oil separator?
A. To capture oil and prevent it from traveling throughout the system
- Blended refrigerants should be charged into a running system
B. As a liquid through a throttling valve into the low side
- 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
- To achieve peak efficiency and performance in a capillary tube system,
D. The system must be critically charged
- Expendable refrigerant means
D. It can be used one time
- 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
- “Pump down” means to capture system refrigerant in the
C. Condenser and/or liquid receiver
- What is the normal operating position for a compressor service valve?
B. Back seated
- The suction accumulator prevents flood back from which of the following?
C. Flooding after hot gas termination
- When the compressor service valve is back seated, which port is closed?
C. Service port
- When work on a refrigerator is complete, the compressor service valves should be in what position?
A. Back seated
- What type of oil is used with HFC refrigerant?
A. Alkyl-benzene
- On an expansion valve refrigeration system, a low pressure control can indirectly be used for
D. Controlling box temperature
- What valve is used to connect multiple evaporators of different temperatures to a single compressor?
B. Evaporator pressure regulator (EPR)
- What valve is used to prevent evaporator pressure from falling below a set limit?
B. Evaporator pressure regulator (EPR)
- What valve is used to control excessive pressure entering the compressor during a hot pull down?
C. Crank case pressure regulator (CPR)
- The oil return orifice inside a suction line accumulator is designed to
C. Meter liquid refrigerant and oil at acceptable rate
- Why do suction line filter dryer’s have two service ports?
B. To enable checking pressure drop across the dryer
- A thermostatic expansion valve (TXV) that creates an unstable suction pressure is said to be
C. Hunting
- Head pressure control valves permit hot gas to travel directly to the
B. Evaporator
- Liquid slugging of the compressor can be caused by
B. TXV hunting
- A severe evaporator freeze up may cause
C. Liquid flood back
- The oil separator is installed in the
B. Discharge line
- If an oil separator is not used,
A. Oil traps should be installed in all vapor carrying lines
- The relationship between low side absolute pressure and high side absolute pressure is called
C. Compression ratio
- If a system has a long suction line riser, an oil trap should be installed
D. Every 15 to 20 feet of vertical rise
- Capacity control of a large compressor can be performed with
C. Unloaders
- Vibration eliminator’s should be installed _______ to the compressor crankshaft centerline.
A. Perpendicular
- What pH level is considered neutral and desired for ice machine or cooling tower applications?
B. 7
- On a rack of multiple compressors, each compressor is controlled by
D. CPR valve
- Which refrigerant line is most sensitive to improper sizing?
A. Liquid line
