Heat & Phase Change
Heat which causes a change in temperature of a substance without a phase change is called what?
Sensible heat
What is the recommended residential indoor relative humidity target for summer operation?
40%
A scroll compressor moves refrigerant through the system by means of what mechanism?
Involute spirals
What is the correct sequential order of steps in the standard vapor-compression process?
Compression, condensation, expansion, vaporization
Zero psig (pounds per square inch gauge) is structurally equivalent to what relative benchmark?
Atmospheric pressure
Heat added to the refrigerant in a vapor state after the evaporation process is completed is called what?
Superheat
What is the temperature at which moisture will start to condense from the air called?
Dew point temperature
What is the purpose of a crankcase heater installed on a compressor?
To prevent refrigerant from migrating to the compressor during the off-cycle
In a direct expansion (DX) system, the refrigerant enters the inlet of the evaporator as what?
A mixture of liquid with some "flash-gas"
Refrigerant R-134a vapor enters the condenser at 124 psig and 100°F. If it leaves sub-cooled by 20°F, the leaving liquid pressure will be approximately what?
124 psig
A refrigerant gives up its latent heat during which part of the cycle?
When it condenses
Frost formation on the suction line indicates that the line temperature is below the dew point and below what threshold?
32°F
Which of the following conditions can cause destructive liquid slugging in a reciprocating compressor?
Liquid refrigerant returning to the compressor
What is the exact state of the refrigerant entering the inlet of the condenser?
High pressure / highly superheated vapor
f a 30-pound cylinder of reclaimed R-410A has stabilized overnight at a room temperature of 70°F, its internal pressure should be approximately what?
201 psig
What is the standard unit for measuring the quantity of heat in a substance?
The British Thermal Unit (Btu)
In the evaporator, what type of heat transfer occurs from the refrigerated space into the refrigerant?
Latent heat is transferred from the space to the refrigerant
Which of the following electrical or thermal conditions would cause a compressor motor to overheat?
High superheat
The refrigerant leaves the exit of the evaporator coil in what standard state?
Low-pressure vapor
The flow rate of a TXV specially designed for R-410A systems compares to an R-22 valve in what way?
It is approximately 15% greater
What is defined as the cooling of liquid refrigerant below its condensing temperature?
Subcooling
When a small air conditioner has an insignificant refrigerant pressure drop through the evaporator, what type of TXV equalizer can be used?
An internal equalized thermostatic expansion valve
What steps should a technician take if a semi-hermetic compressor continuously trips on its internal overload?
Check for electrical problems
Water will vaporize at a surprisingly low 10°F when subjected to what specific vacuum level?
28 in Hg vacuum
Flammability is fundamentally considered a thermodynamic property of a refrigerant? T/F
False