Refrigeration Flashcards
What are the 4 components in a basic air conditioning system?
Compressor
Evaporator
Condenser
Liquid metering device
Which component absorbs heat?
Evaporator
Define a cooling system?
It is a system that takes heat from where it is not wanted and relocates it to where it does not matter
What percentage is relative humidity?
50%
What percentage of liquid and vapour leave the metering device?
75% liquid
25% vapour
What is the compressors job in a refrigeration cycle?
It pumps the refrigerant through the system by establishing the two pressure levels necessary for efficient operation of the system
What happens to the refrigerant as it travels through the evaporator?
It enters as a liquid and leaves as a gas
Name 3 types of condensers?
Air cooled
Water cooled
Evaporative
Name 3 types of metering devices?
Thermostatic expansion valve (TXV)
Capillary tube
Orifices
How is a TXV controlled?
By a sensing bulb attached to the piping on the discharge side of the evaporator
How is a capillary tube used as a metering device?
It reduces pressure from the high side of the system to the low side because of its length and proper bore size
Can a capillary tube be modified or adjusted?
No
What type of metering device allows the system to equalize pressure when the compressor is off?
Orifice
What type of piping is used in air conditioning?
Copper, type K-thick wall
Copper, type L-thin wall
Both are available in drawn temper which is hard or rigid and annealed temper which is soft or flexible
What removes contaminants that may be present in the refrigerant stream?
A filter dryer
How is a filter dryer installed?
With arrows pointing toward the direction of refrigerant flow
How many btu’s per hour is needed to melt one ton of ice at 32 degrees?
12000 btu’s
What is the atmospheric pressure at sea level?
14.7 psi
What happens when a liquid is cooled below 0 degrees but does not change state to ice?
Sub cooling
What happens to a liquid above 212 degrees F but does not change state to steam?
Super heat
What happens to the temperature in refrigerant if you increase the pressure?
Temperature increases
What happens to pressure in refrigerant if the temperature decreases?
Pressure decreases
Where do you find the discharge line on a split system?
Between the compressor and condenser
What is the line between the condenser and metering device called?
Liquid line
The line from the evaporator to the compressor is known as what?
Suction or vapour line
What size of system can licensed sheet metal workers install and service?
5 tons or 60000 btu’s
What does CFC stand for?
Chlorofluorocarbon
What capacity should a recovery cylinder be filled to?
80% maximum
When the refrigerant leaves the condenser it is a hot, high pressure?
Liquid
How many pressure changes will a refrigerant undergo in a complete cycle?
Two-liquid to vapour
What happens to the temperature of refrigerant if it is released into the atmosphere?
It drops instantly
What removes moisture from the air by condensing the moisture onto a cold surface?
Dehumidifier
What components are found on the high side of the system?
Discharge side of compressor, condenser and piping to the metering device
What components are found on the low side of the system?
Discharge side of metering device, evaporator, piping to the compressor and the inlet side of the compressor
What is found in a compressor to help cool it?
Oil- either mineral in older systems or synthetic in newer systems
What type of metering device distributed evenly across the coil?
Orifice
What PPE is recommended when dealing with refrigerant?
Gloves, glasses and face shield
What is the temperature on the low pressure side?
40-45 degrees F
What is the temperature on the high pressure side?
110-115 degrees F
The amount of heat a substance holds is?
Enthalpy
The speed at which heat is released is?
Entropy
What is the temperature of supply air?
55 degrees F
Give 3 examples of an ideal refrigerant?
Latent heat of vaporization should be high
It should not burn or be explosive
It should evaporate at a low temperature and pressure
It should condense at a medium temperature and pressure
Must not be harmful to machinery
Should not be toxic
Why is a TXV the most commonly used valve?
It is the most efficient
What is the greatest method of heat transfer?
Conduction
Where should a filter drier be installed?
In the liquid line leaving the condenser
What is the sequence for refrigerant entering the evaporator?
Refrigerant enters as a high pressure liquid at the expansion valve, moves in one direction through the coil, reaches the sensor for super heat and leaves as a low pressure vapour
When must the filter drier be replaced?
Whenever the refrigeration system needs to be opened for service
How is pressure defined?
As force per unit area
P=F/A
Measured in psi
How is a refrigerant defined?
As a substance used for heat transfer. It absorbs heat by evaporating at a low temperature and pressure and releases the heat by condensing at a high temperature and pressure
When exposed to an open flame, what do refrigerants contain and what can they produce?
They contain fluorocarbons that break down to produce dangerous poisonous vapours
In what 2 components is there a change in temperature of the refrigerant?
Compressor and liquid metering device
In what two components is there a change in state of the refrigerant?
Evaporator-liquid to gas
Condenser-gas to liquid
Where is pressure at or above condensing pressure in the cycle?
On the high side
Where is pressure at or below vaporizing pressure in the cycle?
On the low side
Where is the sensing bulb on a TXV located?
The piping leaving the evaporator
How many BTU’s are required to change the state of water from a solid to a liquid (latent heat of fusion)?
144 BTU’s
How many BTU’s are required to change the state of water from liquid to a gas?
970 BTU’s
Which refrigerants are considered the most harmful?
CFC’s
