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HET4 > Air conditioning fundamentals > Flashcards

Air conditioning fundamentals Flashcards

1
Q

most people feel most comfortable when surrounded by air temperatures of

A

21 - 27 C

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2
Q

why are cabs difficult to heat

A

because of the larger surface area of windows and poor insulation

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3
Q

what is the most desirable cab humidity level

A

40 to 45 %

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4
Q

the purpose of the heater/ air conditioning unit is to

A

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

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5
Q

heat energy always moves from

A

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

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6
Q

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

A

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

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7
Q

what are the three heat movement methods

A

conduction , convection , radiation

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8
Q

what is conduction

A

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

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9
Q

what is convection

A

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

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10
Q

what is radiation

A

is heat movement by electromagnetic rays or moving particles

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11
Q

what are the two methods to measure heat

A

heat intensity and heat quality

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12
Q

how is heat intensity measured

A

by measuring the intensity of molecular motion of a substance

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13
Q

how is heat quality measured

A

by measuring how much heat energy a substance contains

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14
Q

what are the three states of matter

A

solid liquid vapour

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15
Q

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

A

vaporization and condensation

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16
Q

the temperature at which a substance changes state depends on

A

the pressure surrounding the substance

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17
Q

the higher the pressure surrounding the substance

A

the higher the temperature at which the substance changes state

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18
Q

the lower the pressure that surrounds a substance

A

the lower the temperature at which a substance will change state

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19
Q

what is the normal refrigerant used in truck air conditioning systems

A

R-134a refrigerant

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20
Q

what is superheat

A

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

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21
Q

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

A

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

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22
Q

where will most manufacturers run superheat temperatures

A

between 8 - 12 F

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23
Q

what is subcooling

A

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

24
Q

what are the two practical applications for determining subcooling

A

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

25
Q

most manufacturers will run subcooling between

A

12 - 21 F

26
Q

why is it dangerous when refrigerant is exposed into the atmosphere

A

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

27
Q

what is the purpose of oil in the air conditioning system

A

provides lubrication , acts as a sealant and lubricates the compressor

28
Q

what are the four events in an airconditioning system

A

expansion - evaporation - compression - condensation

29
Q

what is the first event in an airconditioning system

A

expansion

30
Q

what is the second event in an airconditioning system

A

evaporation

31
Q

what is the third event in a airconditioning system

A

compression

32
Q

what is the fourth event in a airconditioning system

A

condensation

33
Q

how is the compressor driven

A

by the engine through a clutch pulley

34
Q

what is the compressors function

A

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

35
Q

how is the clutch pulley activated

A

electromagnetically

36
Q

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

A

to avoid mixing R-134a with other refrigerant

37
Q

what is the purpose of the condenser

A

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

38
Q

what are the condenser types

A

tube and fin - serpentine - parallel flow

39
Q

what is the advantage of tube and fin condenser

A

it is the strongest type of condenser

40
Q

what is the advantage of the serpentine condenser

A

high heat transfer in a compact size

41
Q

what is an advantage of parallel flow condenser

A

highly efficient and used when mounting space is limited

42
Q

where are most condensers mounted

A

in front of the radiator

43
Q

what are the functions of the receiver dryer

A

to act as a dryer, filter and temporary storage tank

44
Q

how is moisture trapped in the receiver dryer

A

with use of a desiccant material

45
Q

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

A

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

46
Q

receiver dryers may also be equipped with

A

a sight glass to determine moisture contamination

47
Q

where dose the expansion event take place

A

in the refrigerant metering valve

48
Q

how is the refrigerant metering valve actuated

A

by temperature or pressure

49
Q

what is the refrigerant metering valve designed to do

A

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

50
Q

how is the pressure drop in a refrigerant valve controlled

A

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

51
Q

when the discharge port of the evaporator valve is warm

A

the metering orifice in the thermal expansion valve opens

52
Q

when the discharge port of the evaporator valve is cold

A

the metering orifice in the thermal expansion valve closes

53
Q

when is an accumulator used in a air conditioning system

A

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

54
Q

why should hydraulic hoses not be used in airconditioning systems

A

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

55
Q

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

A

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

HET4 (31 decks)

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