Air conditioning fundamentals

Question 1

most people feel most comfortable when surrounded by air temperatures of

Answer 1

21 - 27 C

Question 2

why are cabs difficult to heat

Answer 2

because of the larger surface area of windows and poor insulation

Question 3

what is the most desirable cab humidity level

Answer 3

40 to 45 %

Question 4

the purpose of the heater/ air conditioning unit is to

Answer 4

provide an air exchange , control humidity , heat and cool the cab and allow fresh filtered air to enter the cab

Question 5

heat energy always moves from

Answer 5

a hotter area to a colder area or from a high heat energy to a lower one

Question 6

how dose the air conditioning system remove hot air from a cabs interior

Answer 6

by moving the heat from inside the cab to the evaporator core ( the cooling element ) and transferring unwanted heat outside the cab

Question 7

what are the three heat movement methods

Answer 7

conduction , convection , radiation

Question 8

what is conduction

Answer 8

heat dissipation by transferring heat energy from one particle to another within and object

Question 9

what is convection

Answer 9

is heat transfer by movement of warm gas or liquids from one place to another

Question 10

what is radiation

Answer 10

is heat movement by electromagnetic rays or moving particles

Question 11

what are the two methods to measure heat

Answer 11

heat intensity and heat quality

Question 12

how is heat intensity measured

Answer 12

by measuring the intensity of molecular motion of a substance

Question 13

how is heat quality measured

Answer 13

by measuring how much heat energy a substance contains

Question 14

what are the three states of matter

Answer 14

solid liquid vapour

Question 15

what are the two important changes of state that happen in a air conditioning system

Answer 15

vaporization and condensation

Question 16

the temperature at which a substance changes state depends on

Answer 16

the pressure surrounding the substance

Question 17

the higher the pressure surrounding the substance

Answer 17

the higher the temperature at which the substance changes state

Question 18

the lower the pressure that surrounds a substance

Answer 18

the lower the temperature at which a substance will change state

Question 19

what is the normal refrigerant used in truck air conditioning systems

Answer 19

R-134a refrigerant

Question 20

what is superheat

Answer 20

when all the liquid refrigerant has gone through a state of change into a vapour and continues to absorb heat energy and will continue to absorb heat with no change in pressure

Question 21

what are the two applications for calculating superheat in an air conditioning system

Answer 21

to determine how well the expansion devise is working and to determine how efficiently the evaporator is working

Question 22

where will most manufacturers run superheat temperatures

Answer 22

between 8 - 12 F

Question 23

what is subcooling

Answer 23

after the refrigerant is completely in liquid form as more heat is removed the refrigerant will drop in temperature without a change in pressure

Question 24

what are the two practical applications for determining subcooling

Answer 24

to be able to fine tune the air conditioning system and to be able to determine the efficiency of the system

Question 25

most manufacturers will run subcooling between

Answer 25

12 - 21 F

Question 26

why is it dangerous when refrigerant is exposed into the atmosphere

Answer 26

because the refrigerant boil away and become vapour and the temperature will drop INSTANTLY causing frostbite or eye damage

Question 27

what is the purpose of oil in the air conditioning system

Answer 27

provides lubrication , acts as a sealant and lubricates the compressor

Question 28

what are the four events in an airconditioning system

Answer 28

expansion - evaporation - compression - condensation

Question 29

what is the first event in an airconditioning system

Answer 29

expansion

Question 30

what is the second event in an airconditioning system

Answer 30

evaporation

Question 31

what is the third event in a airconditioning system

Answer 31

compression

Question 32

what is the fourth event in a airconditioning system

Answer 32

condensation

Question 33

how is the compressor driven

Answer 33

by the engine through a clutch pulley

Question 34

what is the compressors function

Answer 34

it functions as a pump to move the refrigerant and oil through the air conditioning system

Question 35

how is the clutch pulley activated

Answer 35

electromagnetically

Question 36

what is the purpose of the unique R-134a service valve fittings

Answer 36

to avoid mixing R-134a with other refrigerant

Question 37

what is the purpose of the condenser

Answer 37

to transfer cab heat energy to the air outside the truck cab

Question 38

what are the condenser types

Answer 38

tube and fin - serpentine - parallel flow

Question 39

what is the advantage of tube and fin condenser

Answer 39

it is the strongest type of condenser

Question 40

what is the advantage of the serpentine condenser

Answer 40

high heat transfer in a compact size

Question 41

what is an advantage of parallel flow condenser

Answer 41

highly efficient and used when mounting space is limited

Question 42

where are most condensers mounted

Answer 42

in front of the radiator

Question 43

what are the functions of the receiver dryer

Answer 43

to act as a dryer, filter and temporary storage tank

Question 44

how is moisture trapped in the receiver dryer

Answer 44

with use of a desiccant material

Question 45

why is it important to remove water from the air conditioning system

Answer 45

because water can form ice blocking the system , it can cause rust and mix with other chemicals causing acid erosion

Question 46

receiver dryers may also be equipped with

Answer 46

a sight glass to determine moisture contamination

Question 47

where dose the expansion event take place

Answer 47

in the refrigerant metering valve

Question 48

how is the refrigerant metering valve actuated

Answer 48

by temperature or pressure

Question 49

what is the refrigerant metering valve designed to do

Answer 49

to control the flow of refrigerant into the evaporator and create a refrigerant pressure drop at the evaporator inlet port

Question 50

how is the pressure drop in a refrigerant valve controlled

Answer 50

by controlling the size of the orifice in the thermal expansion valve

Question 51

when the discharge port of the evaporator valve is warm

Answer 51

the metering orifice in the thermal expansion valve opens

Question 52

when the discharge port of the evaporator valve is cold

Answer 52

the metering orifice in the thermal expansion valve closes

Question 53

when is an accumulator used in a air conditioning system

Answer 53

when an expansion tube is used in place of a thermostatic expansion valve liquid refrigerant may be able to enter the compressor therefore and accumulator is added to the system in the suction line to prevent this from happening

Question 54

why should hydraulic hoses not be used in airconditioning systems

Answer 54

because their porous construction allows the refrigerant to leak to the outside environment

Question 55

what are the three major differences from fixed orifice tube system compared to the thermal expansion valve system

Answer 55

1 the thermal expansion valve is replaced by a fixed orifice tube 2 the receiver / dryer is replaced by an accumulator 3 the thermostatic switch is replaced by a clutch cycling pressure switch