Pettitech Refrigeration Exam Flashcards
A standard air conditioning system that has low temperature rise across the condenser has…?
Multi answers
Has lost refrigerant and has low charge.
Has poor evap air flow and evap is frozen
Has a metering device problem I.E too restrictive
Suction lines should be…?
Slightly warmer than your SST
(Saturated Suction Temperature)
A high suction pressure can be cause by..?
Multi answers
Metering device too permissive
Clogged condenser coil
High Humidity
What determines system pressure when it has been off for some time?
Ambient temperature at the outdoor condenser
90 deg. F day 410A the pressure will be around 275 PSIG
Liquid lines should be…?
Multi answers.
Slightly warmer than ambient Outdoor air
Slightly cooler than SCT
Noticeably warmer than suction line
Noticeably cooler than Discharge line
Proper use of a vacuum pump?
Multi answer
Remove non condensables
Dehydrate a system
Includes frequent changing of oil
Requires pateint
Includes a Micron gauge
To determine that refrigerant recovery procedure is complete…?
Acheive partial vacuum, close a strand off valve, watch for minimal pressure rise.
True or Flase
Temperature does not reveal the intensity of heat in a substance; it merely tells you its quantity.
False
Proper Subcooling is an indication that…?
Multi answer
The condenser did its job
System charge is correct
The heat that must be released by the condenser is…?
Multi answer
Latent heat
Absorbed heat (Absorbed in the evap)
Heat of compression(HOC)
Sensible heat
Superheat is found in…?
Multi answer
Suction line
Discharge
Superheat is heat that..?
Is added after complete vapourization
Latent heat is…?
Causes a change of state
When air gains moisture, assuming its DB remains constant.
Multi answers
Its WB rises,
RH Rises
and DP rises
It has gained latent heat
When a pipe has condensation on it…?
The dew point of the ambient air is high than the pipes temperature
When Capacitors are connected in parallel…?
The individual MFD is the sum of the individual ratings
5mfd+15mfd in parallel =20MFD
For PSC motors, the capacitor is…?
A run capacitor connected in series with the start winding.
Burnt wires are an indication of…?
Multi Answers
A poor connection,
Excessive amperage,
Poor contacts,
Undersizing wiring
What sequence should be used upon discovering a refrigerant leak?
Multi steps
Recover, repair leak,Pressure test, Evacuate, charge, and tag.
What is the problem when the entire equalizer tube for a TXV has sweat all along it?
Multi answer
The TXV is is internally damaged,
Some liquid might be travelling into the suction line,
The valve will function similar to an internally equalized TXV
Which statements are true?
Evap Saturation should be colder than the suction.
The liquid line should be cooler than condenser saturation.
The suction line should be slightly cooler than evaporator supply air
All of those are true.
Thermal convection is…?
Heat causing flow of vapour or liquid due to differing densities
Thermal conduction is…?
The transfer of heat energy through molecular vibration, contact, and collision.
Therma radiation is…?
The transfer of heat energy through electromagnetic waves
Kelvin is the absolute expression of..?
Celsius
Rankin is the absolute expression of…?
Fahrenheit
What would be the Temp. of a substance that has no molecular motion?
Multi answer
-460F
-273C
0R
0K
Absolute zero
Low suction pressure can be cause by..?
multiple answers
A TXV/EXV that is stuck nearly shut,
A piston restriction,
A liquid line kink,
Low airflow,
Plugged Filter drier,
Low return air temp.
Air conditioning high head pressure can be caused by…?
Multi answers
Non-condensibles,
Clogged Condenser coils,
High humidity
On a TXV the high side liquid pressure exerts an_ influence on the valve?
Opening
On a TXV the spring exerts an ____ influences on the valve?
Closing
On a TXV the sensing bulb exerts —— influence on the valve.
Opening
As humidity rises, the air temperature difference across an evaporator…?
Decreases
Clogged air filters cause liquid refrigerant to flow to the comoressor?
True
What is the volume of displacement if a compressor has a volumetric efficiency of 70% and a cylinder diameter of 2” and the piston stroke is 3”?
Use v=3.14(r^2)h
6.59 Cubed
V=3.14(r^2)h
V=3.14x(1^2)x3
V=3.14x1x3
V=3.14x3
V=9.42
9.42xVOL EFF
9.42x0.70
=6.594
When the airflow of an air conditioning evaporator is poor…?
The evap will probably freeze up,
Could potentially send liquid to compressor
When the evaporator airflow is poor the evaporator air delta T dry bulb is??
Increased because the air has more contact time.
When the condenser airflow is poor the evaporator air delta T dry bulb is..?
Decreased because the evaporator pressure and saturation temperature is increased
When the condenser airflow is poor the head pressure is..?
Increased because thermal transfer is poor
When the metering device is too permissive the evaporator air delta T dry bulb is
Increased because the evaporator has less vapour, more liquid
When the metering device is too permissive the subcooling is..?
Decreased because saturation temperature is decreased,
Decreased because the liquid flow rate is increased in the liquid line
When the metering device is too permissive the superheat is…?
Decreased because the evaporator has less vapour, more liquid
When the metering device is too permissive the head pressure is…?
Decreased because the condenser has more vapour, less liquid,
Decreased, because the liquid flow out of the condenser is increased.
When the metering device is too permissive the suction pressure is..?
Increased, because heat of compression increases,
Increased, because more liquid flows into the evaporator
When the metering device is too restrictive, the evaporator air delta T DB is..?
Decreased becausethe evaporator has more vapour less liquid.
When the metering device is too restrictive the subcooling is…?
Increased, because the liquid flow rate is reduced in the liquid line.
When the metering device is too restrictive the superheat is..?
Increased because the evaporator has more vapour, less liquid
When the metering device is too restrictive the head pressure…?
Increases, as theirs more liquid, less vapour
When the metering device is too restrictive the suction pressure is..?
decreased, because there is less liquid in the evaporator
When the system charge is low the txv will…?
The TXV will try to open trying to decrease superheat
When the system charge is low…?
(Multi answer)
The evap can freeze up,
A hermatic compressor will run hot,
Compressor amperage will be low,
System tonnage will be low
When the system charge is low the condenser delta T dry bulb is…?
Decreased because the condenser Saturation temperature is decreased
When the system charge is low the evaporator delta T dry bulb is….?
Decreased because the evaporator refrigerant heat absorption is less latent, more sensible
When the system charge is low the evaporator air delta T dry bulb is…?
Decreased, because the evaporator has more vapour, less liquid
When the system charge is low the subcooling is….?
Decreased because the condenser saturation temperature is decreased,
Decreased, because the condenser has less liquid, more vapour
When the system charge is low the subcooling is…?
Decreased, because the head pressure is low
When the system charge is low the superheat is…?
Increased, because the condenser has more vapour, less liquid
When the system charge is low the head pressure is..?
Decreased, because the suction pressure is low
When the system charge is low the suction pressure is…?
Decreased, because there is less liquid in the evaporator.
Name a HCFC?
Hydrochlorofluorocarbon, Multi answers
R22
R123
R124
Ozone is…?
Multi answers
Is an active form of oxygen,
Is comprised of 3 oxygen atoms,
In the stratosphere filters solar uv
Is depleted by Chlorine atoms :o
Name a HFC refrigerant?
Hydrofluorocarbon
R134A
R32
R404A
R410A
Their are more types
Which type of refrigerant has not been produced since 1995?
CFC’s
R11
R12
R115
R113
Chlorofluorocarbon
An Azeotropic blend does not change when it…?
Evaporates,
Condenses
A mixture of two/more substances with similar boiling points.
What type of oil is suitable for R22?
Mineral oil
What type of oil is suitable with R134A
POE(Polyolester Oil)
AB(Alkylbensene Oil)
PAG(Polyalkylene Oil)
True or False
Manufacturered Refrigerants are very unique substances that particularly have the uncommon property of being able to become cold when fed into the evaporator. No other substances can behave this way.
False,
Natural refrigerants can exibit the same properties
I.E Ammonia, Carbon Dioxide
Name a CFC’s
Chloroflurocarbon
R11,
R12
R113
R115
Charles law is…?
The gas law describing the relationship between temperature, volume and pressure.
Daltons law is…?
Pressure total= P1+P2+P3,,,,,
The gas law of partial pressures; The total pressure of a mixture of gasses is the sum of the individual saturations pressure
Boyles Law is…?
P1V1=P2V2
The gas law that describes the relationship between pressure and volume, and assumes a constant temperature
