Modern Refrigeration and AC Flashcards
When liquid refrigerant enters the evaporator, the refrigerant is suddenly at a (High Temp and High Press, Low Temp and High Press, Low Temp and High Press or High Temp and Low Press)?
At a low pressure and a high temp
What is used to control the capacity of a commercial compressor?
Unloaders
All of the following effect the capacity of a TXV (thermostatic expansion valve) except an ____________ ________________.
An external equalizer
What system uses a silicone carbide igniter?
Hot surface
What is the process of expanding or enlarging a copper tube to receive another copper tube?
Swaging
All are true of a muffler except…
Can be installed only on intake of compressor
What device prevents slugging in a heat pump system?
Accumulator
Type of circuit where components are arranged in ladder like arrangement?
Parallel circuit
A starter relay drops which of the following out of the circuit?
Start windings
Thermal device that opens its contacts when motor heater coil uses too much voltage is called a _____________ _________.
Thermal relay
How do cooling towers cool?
By evaporation
What color is a dot in a moisture site gage system when indicating a dry system?
Green
A suction line riser should have a trap installed at the lowest point to….
provide reservoir for oil that drips down riser
A yellow tip flame indicates a lack of primary ______ when burning fuel gases in a furnace
primary air
What determines defrost termination on a heat pump system using time initiated, temperature terminated defrost cycle?
Outdoor coil
What does white smoke from an oil burner indicate?
Lein oil and air mixture
Highest temperature at which substance may be liquefied regardless of pressure?
Critical temperature
What rating measures furnace efficiency?
AFUE
What is the purpose of a condenser?
Cools refrigerant to desired temperature
From the expansion valve, the external equalizer runs to…
The outlet of the evaporator
Raising superheat will ____________ an evaporator?
Starve
A device without moving parts that converts ac voltage to a different voltage is called a _________________.
Transformer
Control for refrigeration unit is set to cut in at 45 degrees and out at 35 degrees. If the setting is changed to 45 degrees cut in and 36 degrees cut out, the compressor will have to… (Run less and cycle more or OR run more and cycle less?)
Run less and cycle more
A tech finds discharge pressure on a fully charged system is low due to low ambient temperature. How do you resolve this?
Install low ambient fan control
The pressure in a system is 32.5 PSIA, what is the gauge pressure? (17.8, 32.5, 47.2 or 61.9)
17.8
A manual switch bears markings “1” and “0”. What does this indicate?
On/Off
What is a type of condensing temperature control?
Fan cycling switch
Oil from a hermetic compressor is tested and found to contain acid. This means the compressor has ________________ motor windings.
deteriorating motor windings
What controls refrigerant migration in a single compressor, multiple evaporator system?
Check valve
What is the unit of current or rate of flow of electricity?
Amps
Instrument used to measure relative humidity by comparing wet bulb to dry bulb is called a…
Psychrometer
What is required when multiple A/C condensing units are installed outside and evaporators are installed at a different location in building.
Evaporators must be marked and individually identified
If required, a refrigerant relief vent is usually located at the ________ ______________.
liquid receiver
Pressure gauge of r22 system reads 248 psig and actual line temperature is 100 degrees. What is the amount of subcooling? (12, 14, 16, 18 degrees)
16 degrees
What component of a high efficiency gas furnace is not found on a mid-efficiency furnace?
Secondary heat exchanger
What kind of circuit has infinite resistance and no current? (Open, Closed, Shorted, Grounded)
Open
How many BTU is required to heat 20 lbs of water from 45 degrees to 85 degrees?
800 BTUs
page 45
The low side of a refrigeration system is characterized by (Evaporator, Suction line, Accumulator)
Suction Line
Page 132
Condensers remove heat from the refrigerant that it picked up in the evaporator. True or False
True
What controls an automatic expansion valve?
Evaporator pressure
What is the purpose of an evaporator pressure regulator?
To keep the evaporator pressure above a predetermined point.
The capacity of a TEV varies according to all of the following except which of the following: (orifice, pressure differential between high and low side, temperature and condition of the refrigerant in the liquid line, external equalizer)
External equalizer
What electrical device converts alternating current to direct current?
Rectifier
How do you measure alternating current of a circuit with a meter?
Connect the meter in series
What is the latent heat load in BTU/h of air at 1,500 CFM and the absolute humidity difference is 28 grams?
28,560 BTU/h
Formula is (0.68 x cfm x grains per pound of dry air)
Sensible heat is a measurement of ____ bulb.
dry bulb
What is the possible cause of a yellow flame?
Lack of primary air
Where is the oil pressure safety cutout located?
Connected to the oil pump at low pressure side
In an HVACr system’s refrigerant drier, a substance that collects and holds moisture is called a ___________. In dehumidification, a hygroscopic substance that absorbs moisture from the air.
Dessicant
The transfer of heat from one place to another by means of a liquid to a gas is __________.
Convection
The flow of heat between substances by molecular vibration is called ________________.
Conduction
The specific heat capacity for air is ___._____ BTU/Lb F
0.24 BTU/Lb F
