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HET4 A/C > 403B HVAC CONTROL SYSTEMS > Flashcards

403B HVAC CONTROL SYSTEMS Flashcards

1
Q

Different types of control systems

A
  • Active
  • Passive
  • Combination and suplemental control devices
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2
Q

Explain Active controls

A

They’re re used and controlled by the driver to turn the system on adjust temperature, air flow and velocity.
it would include switches, knobs, levers air louver and if diffusers

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3
Q

Describe passive controls

A

Regulated flow of refrigerant or coolant without driver input.
Examples would be thermostatic switch, pressure activated or regulating valves, pressure and temperature switches

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4
Q

How do you measure air velocity

A

Cubic feet per minute, or CFM

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5
Q

Combination and supplemental control devices

A

They support or prevent functions that effect system operation.
Examples are ambient temperature sensor, multi function pressure switches, radiator fan clutches, radiator shutters system.

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6
Q

What is the purpose of a flow restrictor

A

It is inserted inside some engine cooling water valves.
Slows the engine coolant down so that the heat contained in the coolant has time to transfer heat into the cab interior through the heater core

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7
Q

What device must be installed to prevent hotspots in the engine??

A

H valve

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8
Q

What would happen if the voltage sent to a 12 V stationary electromagnetic clutch coil was too low?

A

The drive plate may slip on the surface of the compressor drive pulley

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9
Q

What is to be noted if the voltage was higher than 15 V in a 12 V stationary electromagnetic clutch coil System?

A

The electrical components of the electromagnetic clutch may overheat

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10
Q

Coolant water valves for part of an active control system that allows the operator to set temperature pass through the heater core

T/F

A

Through the engine coolant water valve is an active control

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11
Q

What colour labels 12 V on electromagnetic clutch coil

A

Black coil lead

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12
Q

What colour indicates a 24 V coil on an electromagnetic clutch?

A

Green coil lead wire

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13
Q

Describe the operation of passive or automatic controls

A

The energizing current must travel through several temperature and pressure sensitive switches before reaching the compressors electromagnetic clutch

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14
Q

What temperature must the compressor reach to cycle off on TXV systems

A

15F

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15
Q

At what temperature will the compressor cycle off on a orifice tube system

A

20F

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16
Q

What is the purpose of a thermostatic switch

A

It prevents The evaporator from freezing up

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17
Q

What types of thermostatic switches are available to us?

A

Adjustable or fixed

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18
Q

At what temperature will a fix thermostatic switch operate

A

32 to 38°F

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19
Q

True or false

The thermostatic switch that is adjustable will always open the switch contacts at a temperature normal worth and 32°F

A

True, the closing of the contacts however can be adjusted to range up to 50°F

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20
Q

How are the low pressure switches connected with the compressor’s electromagnetic clutch?

A

They are connected in series

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21
Q

What happens if the charge at the AC system is lower than 30 PSI on the high side?

A

The compressor is not allowed to operate because of the lack of oil

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22
Q

What happens to the low pressure switch in low ambient temperature?

A

The low pressure switch keeps contact open and the AC system will not operate

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23
Q

Where is the thermostatic switch capillary tube placed?

A

It is placed between the fins of the evaporator

24
Q

What type of air conditioning system will we find a thermostatic switch?

A

Thermal expansion valve

25
Q

What type of low pressure switch is used in an orifice tube type of air conditioning system?

A

Clutch cycling switch;

CCOT Cycling switch

26
Q

Where is the clutch cycling switch located?

A

It is located in the accumulator and it senses the low side of the air conditioning system refrigerant pressure

27
Q

I need TX V system where would you find a low pressure switch?

A

On a TXV system a low pressure switch is used on the low side to protect the compressor from frozen expansion valves

28
Q

How would you describe a low pressure sensing switch, is it a normally open or normally closed switch?

A

Normally open

29
Q

What do we use high-pressure cut out switch is for?

A

High-pressure cut out switches are installed to protect the air-conditioning system compressor from high discharge pressures and temperatures

30
Q

What precautions must be taken when installing a high-pressure switch?

A

The pressure settings of the high-pressure switch must be adjusted lower then the refrigerant pressure relief valve or fusible plug

31
Q

Why is that precautions taken on high pressure switches?

A

It is done so that the compressor electromagnetic clutch coil will not be energized at refrigerant pressure and temperatures that would cause the release of refrigerant into the atmosphere

32
Q

How would you describe a high-pressure cut out switch?

A

Normally closed with normal reference pressures

33
Q

Where would you find a heat sensing switch?

A

They are to be installed on AC tubes or back of the compressor.
They work on temperatures that directly relate to high pressures.
They open at 200°F and they’re usually on the vapour line as it enters the condenser

34
Q

What is the purpose and where would you find a two function binary pressure switch?

A
  • This assembly may be installed on the liquid side of the air conditioning system between the condenser and the expansion valve orTXV.
  • The binary switch acts like a low pressure switch and prevents the compressor from opening if there’s no refrigerant in the system or ambient temperatures are too cold
35
Q

True or false:
The binary switch acts as a high-pressure switch and de-energizes the compressors electromagnetic clutch if refrigerant pressures increase to unsafe levels

A

True

36
Q

What are the three functions of a trinary switch?

A
  • Low range prevents compressors operation if too cold or refrigerant is lost
  • Hi range disengages compressor if refrigerant pressure gets too high
  • Mid range activates engine fan or radiator shutters to draw air through the condenser to lower high side pressure’s
37
Q

Mention two different types of refrigerant flow controls:

A

•Thermal expansion valve
&
•Fixed orifice expansion tube

38
Q

What signals operate the thermal expansion valve?

A

Evaporator temperature in refrigerant pressure

39
Q

What controls the fixed orifice tube?

A

The pressure of the air conditioning systems high side controls the flow of the refrigerant through the fixed orifice tube

40
Q

What component is used for the sleeper compartments to split and direct part of the refrigerant flow to the second evaporator expansion device?

A

Refrigerant solenoid valve

41
Q

What two types of motors do we have in the HVAC blowers?

A

Double entry or single entry blower wheels

42
Q

What electrical device is used an HVAC systems to control fan or blower motor speed?

A

A resistor

43
Q

What electrical device do we use in HVAC to divide the electrical current flow when circuit demand exceeds the capacity of the control switch?

A

Relays

44
Q

What are three distinctive units that are very independent in the heating ventilation and air-conditioning system?

A

AC system
electrical system
cab heating system

45
Q

What happens if refrigerant pressure is high and the road speed of 8 to 45 km/h?

A

The condenser fan is engaged for 90 seconds

46
Q

what happens If the refrigerant pressure is high and the truck road speed is 48 km/h or greater?

A

Condenser fan is engaged for 45 seconds

47
Q

What happens If therefrigerant pressure is high and the park brake is set when road speed is zero?

A

The condenser fan will engage until park brake is released

48
Q

What happens pressure in the system is high in the truck road speed is less than 8 km/h?

A

Condenser fan will engage for 180 seconds

49
Q

What is another name for a manual climate control HVAC system?

A

Temperature blend air door system

50
Q

Which system has the evaporator and the heater core sandwiched together?

A

Integrated climate control system

51
Q

Describe an integrated control system

A
  • Heater water valve controls flow of coolant through heater core.
  • Air flows through the evaporator and heater core assembly.
  • Temperature of the outlet air depends on the amount of cooler passing through the heater core
52
Q

Describe manual climate control system

A
  • Continuous flow of coolant through heater core.
  • Temperature blend air door directs airflow after it leaves the evaporator without water valve.
  • Temperature of the outlet ear depends upon the amount of airflow that passes through the heater core
53
Q

How can we actuate manual climate control doors?

A

Vacuum, compressed air, electric motors

54
Q

True or false

The cab and sleeper air conditioning system do not share the same compressor condenser and receiver dryer

A

False, all of the above mentioned are shared

55
Q

How much diesel do fuel fired air heaters use?

A

Fuel fired heaters use less than a quarter of a litre of diesel fuel per hour and draw less than 2 A per hour of DC 12 V

56
Q

What’s a simple way of describing an auxiliary power unit

A

It’s a complete standalone powered heater unit

HET4 A/C (3 decks)

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