What is the purpose of any refrigeration system?
To move heat.
True or False "cold" is an energy form.
False, cold is the absence of heat.
True or False heat travels faster to cold than it does to warm surfaces.
True
When do liquids boil to a gas?
When they absorb large amounts of heat.
When do gasses condense into a liquid?
When they give off large amounts of heat.
True or False, when something is boiling or condensing the temperature remains the same.
True
True or False, pressure controls when liquid boils.
True
What is the job of the condenser?
To reject heat.
What does the metering device do in the refrigeration system?
Controls the flow of refrigerant to the evaporator coil.
What is the main purpose of a TXV metering device?
Adjusts to varying load conditions and maintains a constant superheat.
What is the purpose of a 410A evaporator?
To absorb heat into the refrigeration system.
In what state does the refrigerant enter the evaporator coil?
Saturated mixture. (Low pressure, low temperature, liquid vapor.
Where does the superheat stage of the cycle take place?
At the end of the evaporator coil after all the liquid has boiled off.
Give two reasons why we add fins to our coils.
To increase surface area and direct airflow.
What is the design return air temp for HVAC equipment?
70-80 degrees
Hermetic compressors steel shell prevents what?
Field servicing
Semi hermetic compressors are field serviceable by virtue of what?
By its bolted construction
Why are rotary compressors more efficient than reciprocating compressors?
They do not have any clearance volume space.
Name two types of rotary compressors.
Rotary blade and rolling piston
How do you figure out compression ratio?
Add 15 to both high and low pressures then divide high pressure into low pressure.
True or False, system efficiency drops as compressor ratio increases.
True
How many BTUs are in one ton of cooling?
12,000 BTUs
Where is the discharge line on a scroll compressor?
Towards the top of the compressor.
Where is the suction line on a reciprocating compressor?
Towards the top of the compressor.
How does a reciprocating compressor compress refrigerant?
By using a cylinder, piston and connecting rod.
Which is a more efficient compressor - reciprocating or scroll?
Scroll, because it does not have trapped re-expansion gas.
What is clearance space in a reciprocating compressor?
The space between the piston and the valve plate.
Define superheat.
The amount of heat added to a gas above its saturation point.
Define Sub-cool.
The heat removed from a liquid below its saturation point.
What is the only thing all compressors must pump?
Vapor
What is not a major type of compressor by mechanical design?
Absorption
True or False, positive displacement compressors move gas by taking gas into a space and then replacing that space with something physical, like a piston.
True
Name three types of positive displacement compressors.
Rotary, scroll, screw and reciprocating.
What kind of compressor is a centrifugal compressor?
Non-positive displacement compressor
True or False, the function of the compressor within the refrigeration cycle is to pump the refrigerant vapor by raising the pressure and temperature of the refrigerant to a saturation temperature above the temperature of the condensing medium.
True
What does not affect compressor capacity?
Time of day
True or False, the intake ports on low and medium temperature compressors are smaller in size than the intake ports on air conditioning compressors because air conditioning compressors have to be larger to allow enough high density, high pressure refriger
False
True or False, hermetic compressors are designed for specific applications because the match of the motor and compressor is dependent upon the factors affecting compressor capacity.
True
Is more or less horsepower required to produce a ton of cooling at an evaporator saturation temperature of 0 degrees F?
More
The purpose of the shaft seal on an open compressor is to...
Prevent oil and refrigerant leaking out of the compressor.
Two advantages of an open drive compressor are...
The motor and compressor can be replaced separately and the heat of the compressor motor does not go into the refrigerant.
A hermetic compressor is...
A compressor that contains both the compressor and motor together inside a welded steel housing.
True or False, one advantage of the semi-hermetic compressor design is that it provides the advantages of hermetic compressors but is still field or factory repairable.
True
What opens and closes the valves in a reciprocating compressor?
The pressure difference across the valves.
The clearance volume of a reciprocating compressor is...
The space left between the piston and the valve plate when the piston is at the top of the cylinder.
True or False, rotary compressors are commonly used on window units, refrigerated appliances, packaged terminals air conditioners and ductless split systems.
True
Rolling piston rotary compressors use an offset rolling piston, which seals against a blade that remains stationary and moves in and out of its slot to seal against the...
Rolling piston
A rotary-vane compressor has a large off-center rotating shaft that carries multiple blades in slots that have a reciprocating action as they move in and out following the...
Cylinder walls
Scroll compressors compress gas between two close-fitted spiral scroll members. One is fixed and the other moves (but does not rotate) in an...
Orbital path
True or False, in a scroll compressor, the only rotating part is the motor shaft.
True
True or False, compliance for scroll compressors allows the scroll flanks to maintain close contact and yet the orbiting scroll can separate and unload to pass a small slug of liquid.
True
True or False, hermetic compressors should only be operated in a vacuum.
False
The purpose of compressor capacity control is to improve efficiency and comfort by matching the compressor capacity to the...
Load
A two-step scroll compressor achieves capacity reduction by utilizing a rotating internal plate that opens and closes two drilled ports in the scroll. When these two ports are open, refregerant exits the scroll in the first...
Compression chamber
An electronic control module controls the____volt DC unloading solenoid coil of the two-step scroll.
24
A digital scroll compressor can operate at what two capacities?
0% and 100%
The digital scroll achieves variable capacity due to its ability to switch very quickly between full on capacity to full off capacity. This allows digital scrolls to produce an...
Infinite range of capacity
What is the lowest percentage of full capacity that a digital scroll can be operated?
10%
Name the three different screw compressor types.
Single screw with gate rotor, Dual screw and Triple screw
How are the small gaps on the screw compressor sealed?
Oil flooding is used for sealing.
True or False, the oil separator is very important to screw compressors because the compressor could quickly run out of oil without the oil separator returning oil to the compressor.
True
True or False, on a centrifugal compressor the impeller acts like a fan. Refrigerant enters in the middle of the impeller and is thrown outward by centrifugal force.
True
True or False, a common splash system uses a slinger which slings the oil around the inside of the compressor.
True
What is the purpose of a crankcase heater on a compressor?
To prevent off-cycle refrigerant migration to the compressor crankcase by keeping the oil warm
What ways can you change compressor capacity to match system load?
Cycle multiple compressors on and off, Cylinder unloading, Hot-gas bypass and speed control
Above what temperature do most refrigerant oils begin to break down chemically?
350 degrees F
What is the compression ratio of a compressor with a suction pressure of 110 psig and a discharge pressure of 360 psig?
3 to 1
True or False, It is incorrect to close the suction line service valve to test a compressor because closing the suction line service valve causes the compressor to pull a vacuum on itself. Compressors that are not designed to operate in a vacuum can arc o
True
True or False, if liquid refrigerant enters the compressor, hydraulic pressures will then develop and break compressor parts like valves, valve plates, rods and pistons.
True
Cylinder gas re-expansion is a problem because gas trapped in the compressor clearance space is expanded at the beginning of the suction stroke. This causes inefficiency because new suction gas cannot enter the cylinder until the trapped gas is a pressure
Below the suction pressure
A technician can tell if a failed compressor has been operating at excessive discharge temperatures because...
The valve plate will be dark and discolored.
A technician can determine if an operating compressor is experiencing floodback by checking the suction superheat at the suction line entering the compressor. A system operating with a suction line superheat of ____ or less is probably experiencing floodi
5 degrees
Name four methods of cooling.
Evaporative, thermoelectric, absorption and mechanical compression
True or False, the temperature at which a liquid boils is controlled by its pressure.
True
Why is boiling considered a cooling process?
Boiling requires heat. When a liquid boils, it extracts heat from whatever it is touching.
List the four major components of the compression refrigeration cycle.
Compressor, condenser, metering device and evaporator.
True or False, both the compression cycle and absorption cycle have a high pressure side and a low pressure side.
True
Which two components are responsible for maintaining the high and low pressures in a compression refrigeration system?
The compressor and the metering device.
Which three components are responsible for maintaining the high and low pressures in an absorption refrigeration system?
The generator, the absorber and the solution pump.
True or False, during the operation of an evaporative cooling system, water flows over the media and air is pulled across the wetted media. Some of the water condenses, having been cooled by the air.
False
Where is evaporative cooling the most effective?
Dry climates
Explain how a thermoelectric refrigeration system works.
When DC current is passed through a thermocouple made of two dissimilar metals, one junction absorbs heat and the other releases heat. This is called the Peletier effect.
From the end of the evaporator, through the compressor, up to the beginning of the condenser, the refrigerant is...
Superheated
True or False, superheating the refrigerant leaving the evaporator ensures that no liquid enters the compressor. However, if liquid does enter the compressor it will not damage the compressor because liquid is compressible.
False
In the compression refrigeration cycle, the refrigerant is subcooled from the ____ of the condenser up to the metering device.
Outlet
Why is sub-cooling desirable?
Sub-cooling ensures that no flash gas occurs in the liquid line on the way to the metering device because flash gas in the liquid line reduces system capacity.
True or False, the refrigerant is saturated in the entire evaporator except for the very end. It is also saturated in most of the condenser except for the very beginning and very end.
True
The heat balance in a compression cycle refrigeration system can be explained as...
The heat picked up in the evaporator + the heat of compression = the heat rejected in the condenser.
True or False, the difference between a liquid receiver and a suction accumulator is that a liquid receiver is used after the condenser on the high side. It is designed to allow only liquid to leave. An accumulator is located on the low side just before t
True
True or False, natural draft does not use a fan and works by natural convection only. Induced draft uses a fan to suck air across the coil. Forced draft uses a fan to blow air across the coil.
True
Name four different types of water cooled condensers.
Double pipe, open vertical shell and tube, horizontal shell and tube and shell and coil.
True or False, fixed restrictions and thermostatic expansion valves are the two large classes of metering devices.
True
Which type of metering device provides the most efficient operation?
Thermostatic expansion valve
True or False, when comparing coil design between older, less efficient air conditioning systems and newer high SEER air conditioning systems, new high efficiency coils are physically smaller than older lower efficiency coils. The newer coils use greater
False
Name the three common refrigerant lines found on a compression refrigeration system.
Discharge line, liquid line and suction line.
True or False, the discharge line is the smaller of the two lines going to the compressor.
True
The ____ line and the ____ line connect the inside and outside units of a split system.
Suction line and liquid line
True or False, the refrigeration cycle is called a cycle because refrigerant circulates from one side of the system to the other and back again.
True
True or False, Refrigeration gauges read in psig and are calibrated to read 1 at atmospheric pressure. Changes in atmospheric pressure can change the calibration point and affect the final reading.
False
True or False, a fluid is a substance that deforms and flows under pressure. Examples are liquids and gasses.
True
Define pressure.
Force per Unit Area
True or False, atmospheric pressure is created by the weight of the air in the atmosphere.
True
14.7 psia = ? psig
0 psig
What factors cause atmospheric pressure to change?
Altitude, temperature and humidity
What is the relationship between atmospheric pressure and barometric pressure?
They are two terms for the same thing
The reading on a low side pressure gauge is 65 psig. What is absolute pressure?
80 psia or 79.7 psia
Convert 100 psia to gauge pressure.
100 psia - 15 = 85 psig
Convert a barometric pressure reading of 26 inches Hg to psia.
26 in Hg/2 = 13 psia
Convert a reading of 20 inches Hg vacuum to psia.
30 in Hg - 20 in Hg = 10 in HG/2 =
5 psia
True or False, a vacuum is any pressure more than atmospheric pressure. Mercury columns can be used to measure vacuum by measuring how much pressure has been removed.
False
True or False, liquid column pressures are expressed in inches of mercury for smaller pressures, like the air pressure in ductwork or gas line pressure. They are expressed in inches of water for larger pressures, like atmospheric pressure or vacuum.
False
What is true about fluid pressure?
Fluid pressure is created by the weight of the fluid, the deeper the fluid, the higher the pressure.
What is the pressure at the bottom of a square tank that has a cross section of 5ft squared and is filled with water to a depth of 4ft?
62.4lbs x 4ft = 249.6 then 249.6/144in = 1.732 psi
What is the pressure in psi required to lift water 15ft?
62.4lbs x 15 = 936 then 936/144in = 6.495 psi
True or False, a simple open arm manometer measures pressure by the pressure pushing on one side of the manometer, forcing the liquid in that side of the manometer down and raising the level of the liquid on the other side. The pressure reading is the dif
True
What type of gauge has an oval metal tube that is curved along its length and forms an almost complete circle? One end of the tube is closed and the other end is connected to the pressure being tested. When pressure is applied to the open end the tube ten
Bourdon tube gauge.
This law states: The total pressure in a mixture of gasses is equal to the sum of all the individual gas pressures.
Dalton's Law
What temperature in degrees Fahrenheit would a fixed volume of gas need to be heated to in order to double its pressure if it starts out a t 25 degrees.
50 degrees F
4ft cubed of gas is compressed from 50 degrees F at 70 psig to 2ft cubed with a resulting temperature of 100 degrees F. What is the new pressure?
171.7 psig
Bars are used in many pressure applications by countries on the SI system. How many bars are equal to atmospheric pressure?
1 bar = 14.7 psia
Which is a larger unit of pressure: 1 kilopascal or 1 psi?
1 psi
Pascals law states:
The pressure on a fluid in a container is distributed equally on all surfaces of the container.