AC LOOP OVERVIEW

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AC LOOP OVERVIEW
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AC LOOP OVERVIEW
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AC LOOP PRINCIPLE (2/3)
Energy balance PE PW PC
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AC LOOP CYCLE ON DIAGRAM OF MOLLIER
Pressure
bar
65
60
0
50.0
De-overheat
Sub-cooling
CONDENSATION
60
40
10.0
DETENT
COMPRESSION
20
5.0
EVAPORATION
0
Liquid
Superheat
-20
Saturated liquid
1.0
Liquid Vapour
-40
0.5
Saturated vapour
Vapour
-60
0.2
0.4
0.6
0.8
0.1
0
100
100
400
200
300
500
Enthalpy kJ/kg
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AC LOOP WITH AN EXPANSION VALVE
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AC LOOP WITH AN ORIFICE
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THE CONDENSER TECHNOLOGIES
Serpentin technology
Mechanical assembly
Brazed tubes
Initial technology
Medium performances
High increasing
Available technology
Low performance it disapears
for vehicle with large
High performances
front surface
Low cost
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THE EXPANSION VALVE (TXV)

• EXPANSION VALVE (TXV) - MAIN FUNCTIONS
• Sudden pressure drop High to low pressure
• Control the refrigerant cooling
• Control of the superheat by controling the mass
  flow
• EXPANSION VALVE (TXV) - CRITERIAS OF CHOICE
• Performance max in the car
• Freezing of the evaporator
• Superheat level
• Stability of the system

It is between the drier receiver and the
evaporator, linked to the evaporator
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THE ORIFICE TUBE

• ORIFICE TUBE - MAIN FUNCTIONS
• IDEM TXV BUT NO CONTROL OF SUPERHEAT MASS FLOW
• Orifice Tube
• Air outlet temperature (power)
• Sub-cooling
• Superheat outlet evaporator
• Pressure and temperature outlet compressor

It is always at the evaporator inlet
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THE EVAPORATOR
Between expension device and the compressor. In
the vehicle, it is in the HVAC unit, under the
cockpit.
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THE EVAPORATOR FUNCTIONS

• To supply the required cooling power for the car
  cabin
• The required thermal power is defined during the
  theorical sizing of the A/C loop components. It
  depends on the thermal balance of the car cabine
  and on customers specification
• The evaporator is selected in the Valeo range to
  fit the thermal performance together with de
  contraintes
• economical constraints
• car integration environment constraints

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THE DRIER RECEIVER

• FUNCTION 1
• To supply the expansion valve with liquid
  refrigerant
• To constitute a liquid reserve
• FUNCTION 2 Dehumidification of the circulating
  fluid
• FUNCTION 3 To filter solid impurities
• SOLUTIONS
• Glass fibre disks with a hole for the diver tube
• Or thermoformed bags containing the desiccant and
  the filter, in an annulus

It is between the condenser and the expansion
valve (TXV) in the engine compartment
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THE ACCUMULATOR

• Accumulator functions
• To supply the compressor with entirely gaseous
  refrigerant
• To dehumidify and filter the refrigerant / oil
  mixture
• To ensure that the oil returns to the compressor
  
• Principal characteristics of an accumulator
• system used to separate liquid / vapour
• useful volume
• desiccant mass
• position of the oil return hole

It is between the evaporator and the compressor
in the engine compartment
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TUBES HOSES

• Tubes Hoses Functions
• To transport R134a and limit leaks
• To resist to ambience and To R143A
• R134a pressure temperature
• Ambience temperature and humidity fluid bonnet
• To reduce noise and vibration transmission
• Not to reduce the A/C Loop performances
• to reduce pressure drop / insulate (LP line f.g.)
• Easy to mount on the vehicle (sensors charge
  connection)

They link the different components to make the
refrigerant circulating in the AC loop
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