Air Conditioning Flashcards
What are different types of condensers ?
Tube and Fin
Serpentine
Parcelled Flow
What is the reliever dryers job
Acts like a dryer
Acts like a filter
And as a temporary storage
Thermal expansion Valve (TXV) is operated by what ??
It is operated by temp or pressure change
Ac fittings
SAE and a 45* flare
What 4 events happen in a A/C system
Expansion
Evaporation
Compression
Condensation
What are the 4 different sizes of A/C lines ?
6,8,10,12
What direction does heat energy move in?
from hot to cold
What are the three functions of heat transfer?
conduction, convection, radiation
What is conduction?
the heat dissipation by tranfering heat energy from one particle within and object to another
What is convection?
the heat transfer by means of movement of warm gasses or liquids from one place to another
What is radiation?
heat movement by electromagnetic waves or moving particles
What is heat intensity?
the measure of the amount of molecular motion the substance contains. Also known as temperature.
What is heat quantity?
tells us how much heat energy the substance contains
What does 1 BTU represent?
he amount of energy it takes to raise 1 pound of water 1 degree farenhiet
how many joules does it take to raise 1 kg of water 1 degree celcius?
4.187kj
What are the three common states of matter?
solid liquid and gas
What is latent heat?
the heat that is required to be added or removed to allow a substance to change state without changing its temperature.
What is sensible heat?
another term for temperature. It is the heat that a substance absorbs that changes its temperature
to change 1 pound of water from liquid to gas how much latent heat is required?
970 btu
The temperature at which a substance changes state is dependant upon what factor?
the pressure that it is under
What is a saturated condition?
When there is a only pure liquid and vapour within a closed container. The liquid and vapour are in balance such that any change in temperature will cause the liquid to vapourize or the vapour will condense
What is super heating?
When heat is added to vapour in a saturated environment the temperature of the vapour increases without changing the pressure of the container.
What is subcooling?
When heat energy is removed from the liquid in a saturated environment the temperature of the liquid falls without changing the pressure of the container.
can a vapour be subcooled?
no because that will cause the vapour to condense.
What are the characteristics of refrigerants?
no color and slight odour. Non-toxic and non0flammable (except those that constain HC), non-corrosive, can absorb and move lots of heat energy, have a pressure temperature relationship that allows them to change state at manageable pressures and at the cabs temperature.
How high can refrigerant temperatures be on hot days?
350 psi
What is R-12 chemical name?
dichloroflouromethane
What is the chemical name of R-134a
tetraflouromethane
R-22
monochlorodiflouromethane
duracool 12a
HC blend
What color container is R-12
white
What color container is R-134a
light blue
What color container is R-22
light green
What color is duracool 12a
White
If refrigerants become mixed what is the resulting pressure temperature relationship?
It becomes the average of the vapour pressure of all of the components at the given temperature
What are the three functions of the oil in a air conditioning system?
lubricate, seal, cool
how is the lubricant moved throughout the sytem?
It is mixed with the refrigerant and moves with it
What is meant by calling a refrigerant oil hygroscopic
it absorbs water readilly
What are the three common types of oil
mineral oil (MO), Polyol ester (POE), Polyalylene glycol (PAG)
is mineral oil used in R-134a systems?
no, it will not mix with R-134a
can polyalkelene glycol be mixed with mineral oil?
not at all
can polyol ester oil be mixed with mineral oil or polyalkelene glycol?
in certain proportions
What makes Polyal ester oil good for topping up?
it mixed with other oils and is miscible with most refrigerants
What are the four events in an air conditioning system
compression, condesation, expansion, evaporation
What are the functions of the compressor?
it is an oil reservior, moves refrigerant through the system and adds heat to prevent the vapour from condensing to soon
What is the function of a reed valve?
one allows refrigerant to flow in when the piston moves down and it closes to force the other reed valve to open on the up stroke.
If reed valves become damaged by liquid being compressed what fault will be seen?
gauge readings will flutter.
What are the three types of air conditioning valves?
R-134a service valve, schrader valve, stem valve
does the high side or the low side of a R-134a system contain the smaller service port?
low side
What is the function of a front seated stem valve?
to isolate the compressor to allow for service gauge installation.
What is the function of the mid seat stem valve?
To allow for live testing with the gauge hooked up.
What is the function of the back seat stem valve?
This is the normal system operating postion,
In what postion must the compressor never operate when using a stem valve?
in the front seat condition
What is the function of the condenser?
The refrigerant enters the condesor as a high pressure vapour. As air is draped across the condenser the heat in the vapour is absorbed and the latent heat of condensation is removed allowing the vapour to change into a high pressure liquid.
What are the three types of common condensers?
tube and fin, serpentine, parallel flow
What are the characteristics of the tube and fin condensor?
it has large diameter pipes that go up and down through a series of fins. It is the strongest type and it is easy to clean
What are the characteristics of the serpentine condenser?
flat tubing with multiple passages pass in the same fashion of as the tube and fin but the fins are thicker. It is harder to see a restriction in this system and it is very difficult to clean. It is more efficient however
What are the characteristics of the parallel flow condenser?
It is built in sections and the coolant travels down and back. It is efficient however less durable and provides a higher pressure drop through the core.
What are the advantages of a radiator mounted condenser?
it is less expensive because the engine fan can be used to cool the condenser. Hoses from the compresser to the condenser can be shorter, it is well protected from the weather.
What are the advantages of the remote mounted condenser?
it can be used when there is a lack of room in the engine compartment, there is not enough cooling available for the engine and the condenser, when there is a radiator mounted air to air cooler, or insufficient airflow.
What is the function of the reciever dryer?
dryer, filter, temporary storage vessel.
Where is the reviever dryer located?
between the condensor and the expansion valve
What can moisture in the cooling system cause?
malfunctioning components, corrosion, can form ice at the inlet of the expansion valve, and can form a strong acid when mixed with the oil
What does the XH7 and XH9 rating mean on the reciever dryer?
it indicates that the reciever dryer is compatible with R-134a, both dessicant and usually fittings.
What safety devices can be included on a reciever dryer?
a pressure relief, separate pressure switches, multi function pressure switches
Where is the temperature sensed to change orifice size in an H-block style thermal expansion valve?
at the outlet of the evaporater
When the thermal expansion valve metering device temperature probe is hot what happens to the orifice?
it is opened to allow extra refrigerant to expand and absorb more heat,
What does a T style expansion device used to sense the temperature?
a capilliary tube
if the expansion valve fails what will likely happen?
the compressor will see liquid and likely fail
What is the difference between the internally and externally equilizing t style valve?
externally equilizing has an extra cappiliary tube to control the equilization. Internally equilized has an orifice inside the valve body
What is required on a fixed oriface tube system to prevent liquid from making it to the compresser?
an accumulator between the evaporator and the compressor
how is the temperature in a fixeed oriface tube system managed?
by using a clutch cycling switch to engage and disengage the compressor clutch based on the pressure in the compressor suction line. Usially on the accumulator
What is the direction of flow in an oriface tube?
from the small end to the screen end
Where is a accumulator mounted on a fixed oriface tube system?
it is mounted between the evaporator outlet and the compressor inlet and it should be mounted next to a heat source to ensure the evaportion of the refrigerant
What controls the clutch on a varriable oriface system?
a thermostat monitors the temperature in the evaporator and the operator selects what the range in which the compressor buts out at.
