Quiz Questions Flashcards
When a heat pump is operating in defrost mode, outdoor fan…
Is off
The amount of moisture in the air compared to the amount of moisture the air can hold at the temperature
Relative Humidity
Where will the refrigerant be superheated at the..
Outlet of compressor, inlet of the condenser, the outlet of the evaporator
R-410a cylinder colour
Rose
Pure water boils at 212F at what pressure?
14.7 psia
Refrigerant with low toxicity and no flame propagation is classifaction
A1
A substance that changes from the solid to the vapour state without going through liquid state. Is called
Sublimation
The amount of heat required to raise one pound of water, one degree Fahrenheit
Btu
Technician removes refrigerant from a system and stores it in an approved cylinder, this is
Recovery
Absolute Fahrenheit scale is called the
Rankin scale
What locations is does the saturated pressure correspond to the saturated temperature
Evaporator and condenser
If refrigerant has a quality of 75% it is
75% liquid 25% vapor
Latent heat of vaporization is
The amount of heat required to change liquid to vapour
Refrigerant vapour entering the metering device can be caused by
A restriction in liquid line, a dirty condenser coil, and undercharged system or leak
Fresh air brought into a house for ventilation purposes is usually
Connected to the return of duct system
Suction pressure being low can be caused by
Dirty condenser coil, low charge, low ambient air temp, dirty filter
Refrigerant leaving the condenser will be
(3)
Subcooled, liquid, high pressure
At a constant pressure the volume of gas varies directly at to absoloute temp and at a constant volume, the pressure of a gas varies directly with absoloute temp
This is called:
Charles law
System equipped with fixed orfice metering device has a sudden increase of indoor temp, what will be the effect on superheat if outdoor conditions remain the same
Superheat will increase
Technician found the the evaporator is operating at a very high superheat, they determined the metering device is ______the evaporator
Starving
410a is a near azeotropic blend, you should charge the system…
In liquid state through suction valve
A frosted suction line indicates
The suction line temp is below dee point if the ambient air or below 32F
Describe refrigeration
The process of removing heat from a place it is not wanted and transferring that heat to a place where it makes little or no difference
The liquid and vapour mixture in the condenser is a
Saturated temperature for the high side of the system
The total pressure if a confined mixture of gases is the sum of the pressure of each of the gases in the mixture
Dalton’s law
Water has a density of 62.4 lbs/cu ft. What’s it’s specific gravity
1
The term hygroscopic refers to
Moisture absorbing abilities of a substance
The refrigerant absorbs heat in the
Evaporator and compressor
Temp of gas leaving the compressor
Hot
Like txv, fixed orfice device controls superheat by losing the refrigerant pressure
Fixed orfice does not control superheat
Presssure in a refrigeration system is changed in the
Compressor and metering device
High temp refrigeration is an
AC System
The heat of compression that is generated in the compressor is removed from the refrigerant in the
Condenser
The capacity of a 2.5 ton ac system is
30,000 btu
(12,000 x 2.5)
What is the movement of heat through space called
Radiation
Heat transfer though space is called
Radiation
An external equalizer line on a txv is designed to
Compensate for pressure drop
As refrigerant passes through the metering device, the result is a drop in pressure and temp, with no change in heat content. This is known as
Adiabatic expansion
The amount of heat required to change the temp of one pound of a substance by one degree Fahrenheit
This is know as
Specific heat
What minimizes migration of refrigerant to compressor
Crank case heater
Removing heat from liquid refrigerant, below it’s condensing temp
Subcooling
Static pressure in a full oxygen cylinder is
2000
29” Hg. Vac is equal to
0.46 psia
What symptoms would an ac system exhibit if the condenser coil is dirty
High head pressure, low subcooling
Refrigerant flow into evaporator with a fixed orfice metering device is controlled by
Pressure different between condenser and evaporator
The ozone layer found in the stratosphere is made up of
3 oxygen atoms
Split systems installed with excessive liquid line length and lift, it could case
Flash gas in the liquid line
Cu ft/ lb is…
Specific volume
The volume of gas varies inversely with absolute pressure, provided the temp is constant
What law is this?
Boyle law
External equalizer line should be installed
Downstream of bulb
Evaporator coils for ac are designed to have
(CFM)
350-400 CFM per TON
System designed to have 11F of subcooling this is important to
Prevent vapour from entering metering device
When ordering 7/8” copper tubing the 7/8” refers to the
Outside diameter
Red gauge also know as
Pressure gauge
Proper subcooling is normally an indication of
A properly charged system
A blend of 2 refrigerants that have similar boiling points and do not separate liquid or vapour state is known as
Azeotropic blends
Most residential condensing unit compressor are cooled by
Refrigerant
The temp above which vapour cannot be condensed regardless of the pressure placed upon it is known as
Critical temp (point)
A heat pump the uses reciprocating compressor should be equipped with what device to protect it from possible liquid flood back
Accumulator
What should a pump down system have
A receiver
During operation, the suction line should be
Slightly warmer then the evaporator saturation temp
The temp of the air leaving the condenser is______ then ambient air
Warmer
Amount of air flow per ton is required through the evaporator of an ac system is
400CFM
What not to pressure test with
Oxygen and compressed air
Technician wants to determine amount of sensible heat added to refrigerant above saturation point in the evaporator coil, they would
Perform a superheat check on suction line
A bourdon tube is often found in a
Pressure gauge
Technician has determined that a newly installed refrigeration system is leaking free, before charging the system with refrigerant they must
Evacuate system
Evaporator T.D is the difference between
Air temp entering the evaporator and saturated suction temp
Which valve is a mechanical control the keeps the refrigerant in evaporator from going bellow a predetermined point
EPR Valve
Evaporator pressure regulator
The bulb for txv should be located
On the suction line at the outlet of the evaporator
When installing a resi split system, the ______ line should be insulated
Suction
What meter uses its own power source
Ohmmeter
When defrost cycle is terminated, the evaporator fans will
Delay coming on
Natural refrigerants are
(3)
Ammonia, carbon dioxide and hydrocarbon(propane)
Only vapour is present, it is
Superheated
Only liquid is present, it is
Subcooled
More net refrigeration=
More cooling
Bubble point on the
Liquid side
Dew points on the
Vapour side
Refrigerant will always travel to the
Coldest part
1KW=______btu
3412
3.412 x1000
1HP=______btu/h
2545
3.412 x 745
1W=______btuh
3.412
Dentsity=
Mass- volume ratio(lbs/ft3)
1/specific volume
Volume of 1 pound of gas (ft3/lb)
Specific volume
1 ton of refrigerant per minute
200 Btu/min
1 ton refrigerant per hour
12000 Btu/hr
Low subcooling and high superheat means the systems
Undercharged
Backseat means
Valve is closed
Valve is ________ for pump down
Frontseated
Valves mid seated for
Standing pressure test and evacuation
As compression ratio of compressor is increased due to higher than normal head pressure
Less refrigerant is pumped though system
Refrigerant muffler is installed on the
Discharge line
What valve design helps to increase compressor efficiency by reducing clearance volume
Discus valve
Most hermetic motor windings are cooled by
Cool suction gas
A de-superheating valve in a hot gas bypass capacity control system is designed to
Mia some liquid with the hot gas to cool it down
Changed the pitch and diameter of a pulley will not effect amp draw
T/F
False
As the piston moved down in the cylinder of a reciprocating compressor
Suction valve will open, moves towards BDC, and re-expansion will occur
One form of capacity control to prevent gas from entering the cylinder chamber is
Cylinder unloading
What’s better scroll or reciprocating compressor and why
Scroll, no volumetric loaded from gas re-expansion
As piston moves up in reciprocating comp cylinder
Volume is decreased, pressure is increased
What conditions can lead to higher than normal compression ratios
Dirty condenser, low suction pressure, high discharge pressure
When piston of reciprocating compressor at TDC, but suction and discharge valve are….
Closed
Starting at TDC position, the 4 processes that occur in the cylinder of a reciprocating compressor are
Re-expansion, suction, compression, discharge
Clearance volume for reciprocating compressor
Decreases volumetric efficiency
A compressor which is driven by a variable frequency drive
Can change speed of the compressor
Best location to measure discharge temp to ensure compressor isn’t running too hot
6” from discharge valve (downstream)
Flapper or reed valves are used in the
Reciprocating compressor
Capacity control method unique to scroll compressor
2 stage modulation by using bypass ports to reduce capacity to approximately 67%
What is volumetric efficiency
How well compressors operating compared to theoretical design capacity
Shell and tube type evaporator that has refrigerant passing though the tubs and the shell is full of water is known as
Direct expansion or dry type
Refrigerant leaves metering device as
Saturated mixture of vapour and liquid
Density of air is the
Weight of air per unit of volume
To process refrigerant to new product specifications “off cite”
Reclaiming
What does the condenser do
De-superheats the vapour, condenses the valour, Subcools liquid refrigerant before it leaves the condenser,
Refrigerant entering the evaporator is
Low pressure, cold, saturated
Evaporator TD is the difference between
Air temp entering the evaporator and saturated suction temperature
Enters the compressor as____
Leaves as______
Low pressure, low temperature, superheated
High pressure, high temperature, superheated vapour
Fahrenheit scale where molecular activity stops
-460 F
If temperatures constant, volume of gas increased the pressure will…
Decrease
Suction line pressure and temperature determine
Superheat leaving evaporator
Subcooling important because…
Increases system capacity
Tube-within-tube water cooled condenser operated more efficiently with counter flow, which means..
Refrigerant is flowing through in one direction and water in the other
Condenser split refers to
Temperature of air entering coil compared to the saturated condensing temperature
Functions of condenser
De-superheat discharge vapour from compressor, condense refrigerant to liquid, reject heat from system and subcool liquid refrigerant
Shell and tube condenser is..
Water flows through tubes and are surround by refrigerant in the shell
As water flows through water cooled condensers
Temperature increases
Condenser operates at______ than evaporator
Higher pressure
Condenser rejects
Sensible and latent heat
As refrigerant passes through the condenser is
Gives up heat
Shell and tube condensers must be cleaned
With brush after removing end caps
Varied temperature of wastewater type condenser has an effect on the
Head pressure of condenser
Shell and coil condenser must be cleaned
Chemically
Tube within tube condenser is______ cooler
Water cooled
Refrigerant entering condenser is
Superheated
Air is made up of
78% nitrogen, 21% oxygen, 1% other gases
Comfort enquires
Temperature, humidity, air movement, air cleanliness
Human body runs at about
98.6 F
Density is
Mass of substance per unit of volume lb/ft3
Dry air weighs
0.75 lbs/ft3
Dew point temp is
Temperature which water will begin to condense out of the air
Specific humidity is
Actual amount of moisture in air measured in grains of moisture per pounds of air
Approximate amount of grains of moisture per pound of water
7000 grains
How many cubic feet of air equal to one pound
1/0.075 lbs/ft3= 13.33 lbs/ft3
The spring of a txv is a
Closing force
Automatic expansion valve
Meters refrigerant to evaporator by using a pressure sensing device
Maintains constant pressure in evaporator
When does the AEV valve open
When pressure drops
How to adjust AEC
Clockwise to open
Turning screw into valve increases suction pressure
Capillary tube metering device
Controls refrigerant flow by pressure drop
Diameter and length determine flow
Doesn’t control superheat
Orfice/ piston metering device
Similar to capillary
Txv and atv need
Receiver
Capillary tubes are charged
Critically
Bulb pressure _____ valve
Opens
Evaporator pressure______valve
Opens
What does the 4 way reversing valve do
Allows heat pump to pump heat in 2 directions
For way reversing valve function in heating cycle
Discharge gas is directed from compressor to indoor coil (condenser)
Larger line on heat pump system is called
And functions as
Gas line
Suction line in cooling
Discharge in heating
Smaller line on heat pump is called
And liquid flows
Liquid line
To inside unit in summer
To outside unit on winter
Four port valve with slide mechanism for larger systems
Use pilot operated valve that use high side pressure to push slide
Air to air heat pump resembles
Mode determined by
AC System
Direction of flow
Auxiliary heat required when
Heat pump can’t provide all the heat needed
Balence point is
When heat pump is can pump in exactly as much heat as structure leaking out
Air to air heat pump COP IS
3.5:1
Air to water COP
4:1
for way reversing valve has
2 inlets 2 outlets
Air source heat pump has
2 metering devices
In heating mode, heat pumps gain efficiency as outdoor ambient temp drops
T/F
False
Electric auxiliary heaters for a heat pump are turned on in stages using
Heat sequencers
Defrost mode for air sources heat pump can be initiated by…
Pressure differential, temperature, time
Outdoor coil operates at the_____ in the heating cycle
Evaporator
Filter dryers installed in heat pump system should be of the byflow type or installed with…
Check valves
Metering devices for most heat pumps are piped in parallel with
The check valves (bypass valve)
Indoor coil of a heat pump operates as the_____ in the heating cycle
Condenser
Defrost cycle in heat pump is used to melt the ice that forms on the
Outdoor coil
During defrost, the indoor fan is turned off
T/F
False
Heat pump that absorbs heat from surrounding air and rejects it into are in a different place is an…
Air to air
EEV constantly monitoring superheat based on…
Pressure transducer and temperature sensor
Capacity control for reciprocating compressor can be achieved by using
Unloaders
Micron gauge should be…
Furthest point away from vacuum pump
As compression ratio increase, the volumetric efficiency…
Decreases
The suction valve of a reciprocating compressor opens based on
Pressure differential
Efficiency of reciprocating compressor can reduce due to
Re-expansion of refrigerant in cylinder
Advantage of open drive compressor is…
Motor can be replaced without recovering the refrigerant
The top scroll in a scroll compressor is
Stationary
Digital scroll compressor achieves capacity by..
Momentarily separating the orbiting scroll from the fixed scroll
Suction gas contaminated heat absorbed while it’s in the..
Evaporator
Rotary compressor requires..
2 full rotations to complete 1 compression process
The temperature of suction gas entering the compressor can be described as.
Cool
Clearance volume is..
The space between to top of the piston at TDC and the bottom of the valve plate
Discus style reciprocating compressor design helps to eliminate the re-expansion of gas in cylinder changer
T/F
True
Discus valve is more efficient than reed valve because..
Allows the cylinders to be designed with less clearance volume
Most heat absorbed by suction gas…
Latent
If compressor discharge is too high it will lead too
The oil breaking down and lead to compressor failure
Air conditioning is considered to be a________ refrigeration
High temp
No superheat can cause_____ in the evaporator
Flooding
High superheat can cause _____ in the evaporator
Starving
How many classes of leaks are there?
6
In refrigerant classification chart the higher the number, the higher…
Flammability
I’m the refrigeration classification chart, the B section means…
Higher toxicity
Can you vapour charge with 410a
No, it will fractionate
Because it’s a blended refrigerant
Can you vapour charge R22
Yes.
Because it’s a single component
Can you use a torch to warm up a refrigerant cylinder
No
Blended compound refrigerant series are…
400 and 500 series
Liquid refrigerant can be added through the..
Liquid line or receiver
When charging with blended refrigerant the refrigerant must leave the cylinder as a…
Liquid
Superheat method of charging is used for
Fixed orfice or capillary tube
To charge a heat pump it should be set in
Cooling mode
Subcooling charging method is used for
TXV
Heat pump is more efficient in what mode
Heating mode
Dew point and bubble point are for _____ refrigerants
Zeoptropic
400 series are
Zeotropic
500 series are
Azeotropic
Fractionation is
Part of the blend will epaporate or condense before the other part
What type of oil absorbs moisture
POE
High td means
Low humidity
Four way reversing
Top is:
Bottom middle:
Top: always permanent discharge
Bottom middle: always permanent suction
What causes
Head pressure will go down
Suction will go up
Compression ratio will decrease
Four way reversing valve is leaking
A four way reversing valve with an internal leak can be confused with
Be confused with a compressor not pumping to capacity
Loose bulb leads to
High suction heat (feeling more heat)
Psig of acetalyn tank is
250 psig
Psig of nitrogen is
2200 Psig
Psig of oxygen tank is
2000 Psig
A before O and off you go
Acetylene, then Oxygen
Difference between tube and pipe
Pipes-measured inside diameter (black pipe)
Tube-measured outside diameter (copper)
Pressure(Psig) for torch would be same as
Tip size
Liquid condensate line connects
Condenser to receiver
Velocity is
Ft/min (fpm)
Pipe diameter increases the velocity
Decreases
Visa versa
Temperature is an indication of the:
Amount of molecular activity in the material
When heat transfers by convention, it
Is transported from one place to another by air or liquid
The temperature in the Celsius scale where all molecular activity stops is:
-273C
When a vapour no longer corresponds to to pressure/ temperature relationship, it is known as_____vapour
Superheated
As refrigerant passes through the metering device, the result is a drop in pressure and temperature, with no change in heat content
This is known as:
Adiabatic expansion
While inspecting an AC system, a tech finds the head pressure running significantly higher than normal for the current outdoor temp. They also notice that the liquid line temp and the outdoor temp are the same.
What could be the cause?
System is overcharged
R-value represents
An insulations resistance to heat transfer
As the temperature of a material increases, the molecules in the material
Increase in speed
134a, Vapour enters the condenser at 124psig and 100F, it leaves the condenser at 80F what’s the pressure?
124psig
The role of the metering device in a heat pump is to
Meter refrigerant
If the sensing bulb in txv developed a leak and started to loose charge, the result would be
The evaporator would be starved and superheat would be high
If a system has a restriction in the metering device, a technician should expect:
High superheat and normal subcooling
When the refrigerant enters the evaporator, it is:
At low pressure, cold and saturated
The blue gauge is know as
A compound gauge
Many rating for components in HVAC systems are not completely accurate due to many different operating conditions are called:
Nominal
When do potential relays close
Loss of counter EMF
