125000393 - INTRODUCTION - AIR CONDITIONING CASING AND COMPONENTS

SPECIFICATIONS

INTRODUCTION

Human beings, as a result of primary and secondary physiological processes, alter the air in the environment in which they live because they increase the rate of carbon dioxide, decrease the percentage of oxygen, give off aromatic substances (e.g. by smoking) and increase the concentration of pathogenic bacteria; all of this makes a closed environment less healthy, especially if it is small.One of the solutions for improving these conditions is to use an air conditioning system.

An efficient air conditioning system fitted on the vehicle should therefore control the main environmental factors that determine the physiological well being conditions for people, which are:

  • temperature;
  • humidity;
  • air speed;
  • purity of the air in the passenger compartment.

The variation in the temperature and the humidity of the air in the passenger compartment is achieved by means of the following two systems:

  • manually operated climate control system, which is fitted as standard on the vehicle.
  • automatically operated climate control system (dual zone) temperature and ventilation, available on higher specification vehicles.
The two systems are described below together for the shared components such as, for example, the refrigeration cycle and separately for all the different components such as, for example the air temperature regulation and control systems because on one system the operating logic (heating/mixing/cooling) in two zones of the passenger compartment is far more sophisticated than on a manually operated type system.

Refrigerant fluid

The fluids designed for use in a refrigerant circuit are known as refrigerants. These are fluids which, in addition to having a LOW BOILING POINT at normal pressure should have:

  • A LOW FREEZING POINT, to prevent solidification even in the harshest climates;
  • A HIGH EVAPORATION TEMPERATURE (change from a liquid state to a gaseous state)
  • A LOW CRITICAL TEMPERATURE (maximum temperature above whch it is no longer possible to liquefy the gas, whatever the pressure applied).

In addition, they should not be:

  • EXPLOSIVE AND FLAMMABLE; to prevent danger in the case of leaks inside the engine comparment;
  • TOXIC OR HARMFUL; in order not to cause injury to people;
  • OXIDIZING AND/OR CORROSIVE; in order not to destroy the system component materials;
  • It should also be possible to mix them with the special lubricants used in these systems to ensure the perfect lubrication of all the system constituent components (compressor, expansion valve, pipes, connectors, etc.).
The most environmentally friendly of the refrigerant fluids currently used in automotive systems is the hydro-fluoro-carbon (HCF) CH2F CF3 or R134a.

Oils for refrigerant systems

Oil is needed to lubricate gaskets, seals, washers and other moving parts of the compressor. A certain amount of oil is introduced into the circuit with the refrigerant and is helpful in keeping the expansion valve in top working order. Only special oils which do not produce foam should be used in air conditioning systems. These are highly refined mineral oils from which impurities such as wax, sulphur and water have been carefully removed. Engine oil should not, under any circumstances, be used in air conditioning systems.Always check the recommendations of the compressor manufacturer before adding oil into the refrigerant system.

Main air conditioning system components

The main system components are illustrated in the diagram.
1 - Compressor2 - Pulley with electromagnetic type clutch3 - Condenser4 - Condenser/fan cooling fan5 - Thermostatic expansion valve6 - Drier accumulator filter with reservoir function7 - 4 stage pressure switch (high pressure)8 - Evaporator condensation collection tank9 - Cooling fan10 - EvaporatorA- Pressurized fluidB - Pressurized gasC - Depressurized fluidD - Depressurized gas

Refrigerant circuit (operation)

The aim of refrigeration equipment is to absorb heat from an environment. In order to do this an air conditioner has recourse to certain fluids (known as refrigerants) capable of cooling down (lowering their temperature) and changing state (from liquid to gas) when they are subject to a large drop in pressure, expanding. They are therefore capable of absorbing heat from the environment. When the temperature increases thereby also increasing the pressure, they change state, another time, from gas to liquid, and condense.The first problem is therefore to liquefy this gas which can be achieved simply by bringing it to a temperature below that of evaporation (or boiling) which, as has already been stated, is -26°C at atmospheric pressure for R134a.In order for this to be achieved at ambient temperature which, in our case, may be rather high (in the engine compartment), it is necessary to increase the evaporation point of the gas so that it remains liquid until the moment it is made to expand to produce the desired refrigerant effect.To raise the boiling point of the gas its pressure must be increased, at the same time, decreasing the temperature.In order for this to take place the system requires a certain amount of power. This power, supplied by the compressor, is subtracted from the power produced by the engine.The operating principle of the refrigerant cycle phases in the air conditioning system for a motor vehicle can be summed up as follows.The gaseous R134a refrigerant is drawn in by the compressor at a pressure of between 0.5 and 2 bar and is compressed at a value of between 10 and 17 bar. The boiling point at these pressures is around 60 °C.This fluid, heated by the compression stage at 80 - 100 °C, always in a gaseous state, in the compressor where, through the effect of the cooling air flow (produced by the vehicle moving forward or through the action of the fan) that passes through, reaches condensation point, changing at high pressure to a liquid state.Later on the refrigerant passes through a filter which has three functions: to trap the impurities, absorb the dampness contained in the circuit and work as a reserve reservoir for the actual refrigerant.The refrigerant reaches the expansion valve, where it is introduced into the evaporator where the pressure is around 1.5 atm. (1.52 bar). At this pressure the liquid/vapour system saturated with the refrigerant fluid is in equilibrium at a temperature of about -7 °C. At the same time, the air that passes through the evaporator (through the action of a fan), being at a considerably higher temperature than the refrigerant fluid it contains, causes it to boil and evaporate completely by imparting heat. On cooling, the air deposits some of the dampness it contains on the evaporator fins in the form of droplets which are collected in a chamber and drained off from the vehicle.The cooled and dehumidified air is sent inside the vehicle. The refrigerant is drawn in by the compressor again at the evaporator outlet, thereby giving rise to a new cycle once again.

The route of the refrigerant fluid can be summarized as follows:

  • 1) In the compressor - the fluid coming from the evaporator is gaseous (temp. -5, -7°C, pressure 0.5 - 2 bar). Compression phase - the gaseous fluid is overheated (temp. 80 -100 °C, pressure 10 -17 bar).
  • 2) Condensator - Compression phase: the fluid gives off heat to the outside, cools down and returns to a liquid state (temp. 40 -60°C, pressure 10 -17 bar).
  • 3) Thermostatic expansion valve - Expansion phse - the fluid loses pressure (0.5 - 2 bar, possibly even 3 bar) becomes a gas + liquid mixture; the temperature is low, typical of air conditioning.
  • 4) Evaporator - Evaporation phase - the fluid becomes completely gaseous because the hot air driven by the fan finds itself at a higher temperature than the refrigerant fluid and causes it to boil and evaporate completely giving off heat. The temperature is low, typical of air conditioning (pressure 0.5 - 2 bar).

DUAL ZONE AUTOMATIC CLIMATE CONTROL SYSTEM

The automatic climate control system is managed by a control unit which is capable, thanks to an extremely sophisticated operating logic, of controlling the temperature in two zones of the passenger compartment heating or cooling the intake air to produce the desired comfort level. It is also capable of demisting 60% of the surface of the windscreen and 20% of the side windows in a relatively short time (about 5 minutes) improving driving safety.This can be achieved thanks to the excellent software logic and the optimum air distribution.

System component location

The location of the main components is illustrated.
1 - Air conditioning compressor2 - Pulley with compressor electromagnet coupling3 - Air conditioning condenser4 - Drier filter5 - 4 stage pressure switch6 - Expansion valve7 - Evaporator unit8 - Low pressure connector (BP)9 - High pressure connector (AP)10 - Driver''s setting/equivalent temperature display11 - Interior fan speed display. Fan symbol. OFF12 - Passenger side setting/equivalent temperature display13 - Driver''s temperature selector knob14 - Interior fan speed/OFF control knob15 - Passenger side temperature selector knob

Interior air distribution diagram

The distribution of the air in the passenger compartment is illustrated in the diagram.
1 - Fixed upper diffuser for windscreen defrosting and demisting2 - Adjustable centre upper vent3 - Fixed diffusers for demisting or defrosting side windows4 - Orientable and adjustable central diffusers5 - Orientable and adjustable side windows6 - Fixed front footwell diffusers7 - Fixed rear footwell diffusers8 - Directable and adjustable rear vent

DESCRIPTION OF COMPONENTS

DUCT/DISTRIBUTOR ASSEMBLY

This comprises two modules which contain:

  • the fan
  • the evaporator
  • the upper mixture, distribution and recirculation flap control actuators
  • the heater radiator
  • the lower mixed air temperature sensors.
A section of the assembly is illustrated below
1 - Air intake/recirculation flap2 - Electric fan3 - Evaporator4 - Air mixing flaps5 - Mixing flaps partition6 - Heater radiator7 - Air distribution flaps8 - Additional heater (diesel version)9 - Climate control system node (NCL)A - Recirculation air flowB - Outside air flowC - Windscreen/side windows air flowD - Centre and side vents air flowE - Interior vents air flowThe fan directs the flow of outside air towards the vehicle interior.

The air introduced into the passenger compartment passes through a combination filter composed of two layers:

  • the first "particle" layer has the function of trapping the particles of fine dust and pollen
  • the second "active charcoal" layer traps several pollutant agents present in the atmosphere.
If the recirculation function is activated, the special flap directs the flow of air from the inside of the passenger compartment. The flow of air firstly comes into contact with the evaporator then, partly or totally with the heater radiator, depending on the position of the mixture flap. Lastly, the air is sent to the various vents depending on the position of the upper, centre and lower distribution flaps.All the flaps are operated by electric motors controlled by the control unit.
1 - Electric fan2 - Evaporator3 - Heater radiator4 - Lower mixed air sensors5 - Recirculation flap actuator6 - Mixed air flap actuators7 - Air distribution flap actuator8 - Combination filter element (pollen filter)9 - Air Quality Sensor10 - Fan speed electronic variatorThe upper mixed air sensors are located on the dashboard ventsAll the flaps are activated by special actuators and kinematic systems operated by the control unit.

NCL CLIMATE CONTROL NODE OF ELECTRONIC CONTROL UNIT

The system controls are illustrated in the diagram below.
1 - Compressor on/off control button (orange LED)2 - AUTO button for all functions (2 orange LEDs)3 - MONO button for single/differentiated temperature selection (orange LED)4 - Driver''s temperature selector knob5 - Passenger compartment temperature sensor protective grille6 - Interior fan speed/OFF control knob7 - Air distribution selection buttons (3 orange LEDs)8 - Passenger side temperature selector knob9 - Heated rear windsdcreen control button (amber LED)10 - Air recirculation control button E/I (2 orange-amber LEDs) A = automatic recirculation operation (amber LED)11 - MAX-DEF function control button (amber LED)12 - Passenger side setting/equivalent temperature display13 - Interior fan speed display with bars (fan symbol - OFF)14 - Driver''s setting/equivalent temperature displayThe climate control system has automatic temperature and ventilation control with recirculation.The user can select the desired temperature within the limits of the system.The control unit manages the automatic climate control system temperature in two zones of the passenger compartment.The split automatic climate control system controls the temperature on both the driver and passenger sides throughout the operating range, heating or cooling the air introduced into the passenger compartment to reach the desired comfort level.

The control unit acquires temperature information from the outside air sensor, from the treated air sensors (two upper and two lower), from the passenger compartment internal sensor, from the solar sensor, the misting sensor and the pollution sensor as well as from the body computer (engine rpm and vehicle speed). By processing this data using a special algorithm, the microprocessor carries out the adjustment of the following parameters/funct

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