323001413 - AIR CONDITIONING CASING AND COMPONENTS - GENERAL INFORMATION

INTRODUCTION

The climate control system fitted to the vehicle is used to alter the environmental properties of air taken into the passenger compartment (temperature and humidity), allowing the demisting of the glass surfaces and preventing the intake of pollutant substances, thereby making the environment in the passenger compartment more healthy.The air conditioning system is a comfort factor that contributes to improving the physiological wellbeing of the vehicle occupants.

Climate control system components

The climate control system components are illustrated in the diagram below.1 - Linear pressure switch2 - Condenser3 - Drier filter built into the condenser4 - Low pressure pipe5 - Expansion valve6 - Evaporator7 - Control panel8 - Pollen filter9 - Duct/distributor unit10 - Compressor11 - High pressure gas pipe12 - High pressure fluid pipe

Operating principle

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, thus expanding. They are therefore capable of absorbing heat from their environment. When the temperature increases, thereby also increasing the pressure, they change state again, 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, in order 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 is heated by the compression stage at 80 -100 °C, always in a gaseous state. It is heated 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, it 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, to absorb the dampness contained in the circuit and to 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:- 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).- Condenser - 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).- Thermostatic expansion valve - Expansion phase - 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.- Evaporator - Evaporation phase - the fluid becomes completely gaseous because the hot air driven by the fan is 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).

Types of system

This vehicle can be equipped with different climate control systems for the passenger compartment:- manual climate control- automatic climate controlManual climate control: the user sets the air temperature, distribution and flow rate and they remain like that until they are altered by the user later on.Automatic climate control: the user can set the parameters and select automatic system management. If they so wish, the user can retain the facility to manage the system manually.

MANUAL CLIMATE CONTROL

The manual climate control system control panel is illustrated in the diagram below.A - Air temperature adjustment knob (hot/cold air mixing)B - Fan speed selection knobC - Passenger compartment air distribution selection knobD - Cursor for switching interior air recirculation on/offE - Climate control compressor on/off button (by pressing the knob)

Operation

The manual air conditioning also allows the user to manage the temperature and the intake of air into the passenger compartment using the control knobs and buttons.The following parameters/functions can be altered manually:- Temperature- Distribution in 5 positions- Fan speed- Engagement of compressor- Recirculation.The transmission of the air mixture and air distribution commands from the knobs and the air recirculation from the knob lever to the heater casing takes place by means of transmission cables (bowden cables).The compressor can only be activated if one of the fan speeds is switched on.

COMPONENTS

Air conditioning unit

The unit comprises two modules which contain:- the fan- the evaporator- the heater radiator- the pollen filter- the lower/upper mixed air temperature sensors (for the automatic version)- the flap control actuators.1 - Duct/distributor assembly2 - Outside air intake3 - Recirculation air intake4 - Electric fan5 - Pollen filter6 - Evaporator7 - Heater8 - FLOOR air outlet9 - VENT air outlet10 - DEF air outlet

Automatic climate control unit

The structure of the unit is similar to the manual one and features electric motors, for moving the various flaps, controlled by the climate control system control unit:- recirculation actuator,- air mixing actuator,- air distribution actuator.Temperature sensorsThere are two temperature sensors on the duct/distributor assembly that provide the climate control system control unit with a signal relating to the temperature of the air coming out of the vents. One sensor is located by the FLOOR vents (left-hand side), the other by VENT outlet (left-hand side).There is also a passenger compartment air sensor (housed in the climate control system control unit) and an outside temperature sensor (located in the lower part of the right external rear view mirror).Automatic system operationThe air is drawn in by the fan through the outside air intake or through the internal air intake. It passes through the pollen filter, the fan and reaches the main body. From there it passes through the evaporator and reaches the mixing and distribution area. The temperature of the air to be sent to the vents is determined by the position of the mixture flaps which have the task of shuttering the flow of air coming from the outside directly to the distribution area or the heat exchanger.Solar sensorThe solar sensor is located in the top part of the dashboard at the base of the windscreen and its function is to transform the light signals (lux or kcal/m2) into a proportional linear electrical signal. The sensor is a particular type of diode (photodiode) which can vary its conduction depending on the quantity of light it comes into contact with; in practice, the incident light which comes into contact with the photodiode small lens releases electrons from the crystalline structure.As a result electrons and free gaps appear in excessive numbers.They are directed towards the photodiode spatial or junction zone (NP) and increase the junction current (photoelectric current) in proportion to the intensity of the light. In order to achieve a very high response speed, the photodiode is equipped with a small lens which has the task of improving the focus of the light on the semiconductor junction (NP) which makes up the photodiode.The control unit (NCL) using this signal alters the temperature parameters decreasing it and at the same time acting on the distribution of the air.1 - Solar sensor2 - Output current lighting typical diagram3 - Diagram showing operation of solar sensor

Manual climate control unit

The unit is similar to the automatic one and features the following differences:- no temperature sensors,- mixture and distribution flaps controlled by bowden cables,- resistive type fan speed governor,- manual recirculation

Expansion valve

The section of the expansion valve and the main parts are illustrated in the diagram below.1 - Fluid outlet duct from the evaporator2 - Heat sensitive element3 - To the compressor intake connector4 - Pressurized fluid5 - Counter spring6 - Ball and calibrated port7 - Expanded fluid (at the evaporator inlet connector)8 - Valve body9 - RodC - To the compressorF - To the drier filterEi - Evaporator inletEu - Evaporator outletThe tasks of this valve are to:- Separate the high pressure circuit from the low pressure circuit;- Expand the refrigerant (change in state from liquid to gas);- Regulate the evaporation process (flow rate);- Regulate the evaporation temperature;- Protect the compressor from refrigerant fluid.The thermostatic expansion valve is fitted on the evaporator inlet and outlet ducts with the task of regulating the flow and expansion (drop in pressure) of the R134a fluid before entry into the evaporator.The automatic regulation of the size of the passage for the gas inside the expansion valve is produced by a sensitive bulb which measures the temperature of the refrigerant fluid and depending on this suitably adjusts the size of the opening that the gas passes through by means of a special spring that moves a shutter determining the extent of the expansion.The increase in temperature at the evaporator outlet, detected by the bulb, ensures that the valve is opened with a consequent increase in the flow rate of the fluid in the evaporator.Conversely, low temperatures involve a reduction in the size of the gas port, determining a decrease in the flow of gas.

The valve regulation screw is calibrated during production and should NOT be tampered with, in order to avoid adversely affecting the efficiency of the air conditioning system.

The expansion valve is directly accessible from the engine compartment; see the diagram below:1 - Expansion valve cap2 - M6x22 bolt3 - M5x50 bolt4 - Expansion valve5 - Plate securing valve/pipes6 - Freon pipes seal7 - ValveThis type of expansion valve has two different refrigerant fluid flows:- Lower flow from point (4), gas coming from drier filter, to point (7), outlet of gas to the evaporator, containing the heating spring (5) and the modulating element which in this case is the ball (6) housed in the calibrated duct.- Upper flow, from point (1), gas coming from the evaporator, to point (3), outlet of gas to the compressor, containing the thermostatic sensor (2) which is connected to the top part of the diaphragm and to the ball (6).The control function for the flow rate is exerted by the movement of the ball (6), connected, via the rod (9), to the thermostatic sensor (2).The action of the ball (6) is opposed by the suitably calibrated spring (5) which ensures that the refrigerant fluid in the evaporator is in a gaseous state without the presence of any liquid which, if drawn in by the compressor, could damage it.The position of the ball (6) depends on the difference in pressure acting on the diaphragm located inside the sensor (2); this, in turn, depends on the outlet temperature of the refrigerant fluid from the evaporator (upper flow for the valve).High temperatures for the gas coming out of the evaporator (1) corresponding to high heat dissipation conditions increase the pressure inside the thermostatic sensor (2); this involves the movement of the rod (9) and the ball (6) connected to it, increasing the section of the passage and, as a result, the flow rate of the refrigerant (7).The reverse is true if the temperature of the gas coming out of the evaporator (1) is low.

Linear pressure switch

The linear pressure switch controls the correct operation of the system, replacing the task performed by the quadrinary pressure switch. By continuously analysing the pressure of the climate control system circuit, the sensor provides the engine management control unit, in real time, with the variations in pressure, making the management of the activation levels more flexible.For each variation in pressure there is a corresponding voltage signal used by the engine management control unit to activate the fan speed and switch off the compressor if the pressure increases or decreases beyond the permitted limits (safety function).The operating range of the linear sensor goes from 3.018 bar up to 29.508 bar according to the following pressure (bar) / output voltage percentage (%Vcc) curve.

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