LV35 cooling systems (3)

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kap all phase & 6/11/03 11:35 am Page Student Workbook LV35 Cooling Systems (3) LV35/SWB Student Workbook for Technical Certificates in Light Vehicle Maintenance and Repair MODULE LV35 COOLING SYSTEMS (3) Contents Page Climate Controlled Systems Air Conditioning: Functional requirements Temperature Control – Heating: Air mix type Water flow control type 5 Air Circulation Control: Damper operation (flaps) Push button type Humidity control Relative humidity Air purification 6 7 Temperature Control – Cooling: Latent heat of evaporation Cooling Condensing Liquefying Basic operation of the refrigeration cycle Progress check 10 11 12 14 Main Components 18 14 15 ……… Page Air Conditioning Control: Magnetic clutch Evaporator temperature control Dual pressure switch Gas ejection method Compressor belt protection system Variable speed blower motor 36 36 37 38 39 40 40 Electrical System Overview: Progress check 41 42 Health and Safety Legislation: Refrigerant Recovery and recycling equipment R12 and R134a Health and safety information Legal requirements 43 43 44 44 45 46 Servicing and Repair: Connection differences between R12 and R134a Layout of an air conditioning system Fault chart Blocked condenser fins Drive belt Special service tool 47 (Cont.) -1Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue 47 48 49 50 50 51 Page Sight glass Refrigerant leaks Blower motor noise 52 53 53 Service Recycling Station 54 Pressure Testing: Manifold gauge set Description of gauge Connecting the manifold gauge Refrigerant container tap valve Installing the manifold gauge Evacuating air for the air conditioning system Installing the refrigerant container tap valve Inspecting the system for leaks Leak detection Halide leak detector Adding more refrigerant Fitting a new refrigerant container Normal condition pressures Quick reference flow chart Progress check 56 57 58 58 59 60 61 62 62 63 64 65 66 66 67 Fault Diagnosis using a Manifold Gauge: Progress check 69 76 60 ……… Page Climate Control: Components Description Controls and features Temperature Re-circulated air Automatic blower control Control system Temperature regulation 77 77 77 78 78 79 79 80 80 Types of Sensors: In-car temperature sensor Solar sensors Ambient air temperature sensor Evaporator sensor Coolant (heater core) temperature sensor Airflow control Damper operation (flaps) Push button type Blower motor (interior fan) speed Progress check Progress check 81 81 82 83 83 -2Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue 84 85 87 87 88 89 92 Climate Control Systems Drivers demand a heating system that maintains a comfortable temperature and a steady stream of fresh air Due to the development of motorways and the resulting traffic congestion caused by a more mobile society, drivers are spending more time in their vehicles It is therefore essential in the interests of health and safety that the occupants of vehicles are provided with a continuous supply of fresh temperature controlled air This has lead to very sophisticated heating and ventilation systems being fitted in motor vehicles Air Conditioning Four functions of A/C The purpose of air conditioning is to maintain a comfortable environment inside the vehicle, which includes the following: • temperature control • air circulation • humidity control • air purification -3Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Functional requirements The equipment necessary to provide air conditioning in the motor vehicle consists of a cooler or refrigeration system, heater, moisture controller and a ventilator • the temperature must be adjustable • heat must be available as soon as possible • heat needs to be directed to different areas of the inside of the vehicle • ventilation must be provided with minimum noise • the system must be able to demist all windows • ease of operation is essential for safety reasons -4Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Temperature Control – Heating Varies the amount of air flowing over the heater matrix Varies the amount of coolant flowing through the heater matrix In vehicle heater systems the coolant is pumped through a hot radiator matrix, a blower is used to blow cool air through the matrix causing the air to heat up The engine must be hot for this to happen Two methods are used, one method is air mix and the other is water flow control Air mix type In this type of heater the proportion of cool air is passed over the heater matrix and a proportion bypasses it Water flow control type In this type of system, the flow of water through the heater matrix is controlled by a valve, which causes the temperature of the matrix to be varied Some manufacturers combine the two methods using two heater matrix each with their own coolant control valves, one to supply controlled heat to the driver’s side (right hand valve) and one to supply controlled heat to the passenger side of the vehicle (left hand valve) An electric circulation pump may be integral with the ‘pump valve unit’ as it is known -5Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Air Circulation Control Damper operation (flaps) Water valve control cable Air inlet control cable Control panel Air mix control cable Air flow control cable There are two types of operating methods a manual or lever and a push button type In the lever type, no electric motors are used The driver operates the controls manually, the cables move the flaps as the levers are moved Push button type Air inlet selector switches Air flow selector switches Pressing the buttons on the control panel causes the servomotors to operate the dampers Servomotors are discussed in detail later in this workbook -6Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Humidity control Humidity is the term used to describe the degree of dryness or wetness in the atmosphere, dry air contains no moisture If ice is added to a glass of water, drops of water appear on the outside of the glass as the water is condensed from the surrounding air This demonstrates that humidity is the amount of water vapour contained in the air The cooling process brought about by air conditioning reduces the humidity of the air through this condensing effect Relative humidity Humidity levels are quantified using the term ‘relative humidity’ The relative humidity level of air is a reflection of the amount of moisture that it actually contains compared to how much moisture it is physically capable of containing If we describe the humidity level as being 50%, this means that the air is at half moisture capacity Think of it as being half full! As air is cooled, it becomes denser and therefore less capable of holding moisture A human being feels at their most comfortable when the atmosphere has a temperature of around 22°C and a relative humidity of about 25% -7Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Air purification The air inside the car goes through a process of filtration to ensure that any particulates such as smoke and pollen are removed A reduction in pollen would be seen by hay fever suffers as a major benefit (from a comfort and a safety point of view) These pollen filters must be replaced periodically as recommended by the vehicle manufacturer -8Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Temperature Control – Cooling After swimming water vaporises from the body causing it to feel cool Alcohol or any liquid that will readily vaporise such as petrol, if spilled on the hand, will cause the hand to feel cool This is because heat is extracted during the vaporising process A more scientific way of examining what happens is described If a container is placed in an insulated box (fitted with a tap) and a liquid that will vaporise readily is placed in the container, when the tap is opened the liquid in the container will vaporise as heat is removed from the air inside the box, therefore the temperature of air inside the box falls If the gas is condensed and returned to the container no loss of liquid will result This use of heat energy in order to evaporate is called ‘latent heat of evaporation’ -9Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Controls and features Set to automatic or manual blower control Temperature sensor In car temperature setting Cool down button Air distribution control Increase temperature control button Air re-circulation Air conditioning switch Setting the blower control to auto with the desired temperature selected, maintains the temperature The blower speed slows as the temperature is reached, thus creating an even temperature throughout the vehicle A sensor, which regulates the temperature, is fitted in the centre of the instrument panel Temperature Temperature is adjusted by means of pressing the blue switch to cool and the red switch to raise the temperature some systems adjust in 0.5 degree steps and others in degree steps The recommended comfort temperature setting for all systems is 22°C - 78 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Re-circulated air Pressing the button for re-circulating the air inside the vehicle, toggles between outside air and re-circulated air, this position also shuts out unpleasant odours Air conditioning will automatically switch on to reduce the potential for misting of the windows However the air conditioner can be switched off manually if desired When the air conditioner is on and the interior and exterior temperatures are quite warm, the climate control system automatically selects the re-circulated air position to maximise cooling of the interior Once the selected temperature is reached, the system will automatically change to the outside air position Reducing air humidity (air directed to screen and floor or screen only) Switching on the air conditioning will reduce humidity and accelerate the demisting of windows If air is directed onto the windscreen the air conditioning cannot be switched off, this is to ensure maximum performance of the defrost/demist function Automatic blower control With the blower control in position AUTO and the air distribution control in the screen position the blower will operate at a low speed until the engine is heated up sufficiently to provide warm discharge of air In all other positions the blower will not operate until the engine temperature guarantees that there is sufficient discharge temperature available - 79 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Control system Sensors and controls Actuators Fresh or recirculated air Driver control Hot/cold flap In-car temp sensor Air outlets Ambient air temp sensor ECU AC control Solar temp sensor Heater control Engine speed control Mix air temp sensor Sensors constantly monitor the temperature inside the vehicle and adjustments are made via the ECU (Electronic Control Unit) to the actuators (servomotors) Since the heat from the sun will warm up the vehicle interior, a solar sensor is fitted to adjust the amount of cooling or heating required Temperature regulation Blower Air intake NTC Thermistor Measured in-car temperature is compared with the outside temperature Temperature flaps are activated depending on the results of this comparison This process is continuous and reference is made to additional correction variables for automatic regulation - 80 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Types of Sensors In-car temperature sensor Negative temperature coefficient Positive temperature coefficient The temperature sensor for monitoring the in-car temperature is normally located in the centre of the instrument panel Air is drawn through the sensor air intake by the action of the blower, which passes over the NTC resistance, therefore altering the value of its resistance depending upon the ambient temperature NTC (negative temperature coefficient) means that as the temperature increases the resistance of the sensor falls, unlike the behaviour of a Ureka or Nichrome wire, which has a positive temperature coefficient (PTC) This means that as the temperature increases the resistance increases, a good example of this is an engine manifold heater An alternative arrangement, which utilises the heater blower to draw air through the sensor is shown above - 81 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Operation As the heater blower blows through the aspirator it causes a depression in the narrowing part of the tube, which pulls air from the vehicle interior through the temperature sensor Both systems allow for an accurate reading due to the air continuously being sampled and directed over the sensor Solar sensor Can be fitted on top of the instrument panel in the centre or two sensors may be used, one at each corner On top of the instrument panel is located a photo sensor (photodiode) This monitors the angle and the amount of sunlight entering the vehicle through the windscreen The solar sensor provides the signals used to compensate for the effects of the sun’s rays at the control and display unit (ECU) The solar sensor is enclosed in a scratchproof cover, which is made of tough plastic The cover acts as a filter and allows only infra-red radiation to penetrate it If the sun entering the vehicle is stronger on the right hand side then the climate control system can respond by directing more cooling toward the right side than the left A fail-safe is programmed into the control unit, which ensures a default value is substituted in the event of a sensor failure - 82 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Ambient air temperature sensor Ambient Air Temperature Sensor Thermistor Condenser Resin case The ambient air temperature sensor may be found within the front bumper area two sensors may be fitted If two sensors are used, the lowest temperature signal of the two is used for control function If a sensor should fail then the signal from the remaining one is used If both sensors fail, then a fail-safe mode is adopted (the default temperature is usually in the region of 10°C) The compressor used in aircooling is deactivated and the outside temperature display on the instrument panel will not function Evaporator sensor EVAPORATOR SENSOR A thermistor is attached to the evaporator fins, when the fin temperature drops the magnetic clutch will be turned off thus stopping the compressor (Performs the same task as the anti-frosting device in basic air conditioning) - 83 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Coolant (heater core) temperature sensor WATER TEMP SENSOR This sensor is installed in the coolant feed to the heat exchanger (radiator) for the heater Not all vehicles have this sensor fitted, it depends upon the specification The sensor must not be confused with the coolant temperature sensors used for engine management or the temperature gauge The sensor measures the coolant temperature in order to determine heat availability from a cold or warm engine During engine warm-up the sensor influences air distribution and fresh air blower speed The fresh air blower will run at a considerably slower speed when the engine is cool and the air conditioner is set in the automatic mode By using this method of temperature control, engine warm-up speed is increased and at the same time cold air is prevented from entering the cold passenger compartment Vehicles not having a temperature sensor fitted in the heater core usually have a time function as a replacement, this means that the engine is assumed to be warm after a certain length of time, the outside temperature is taken as a base setting after a prolonged down time - 84 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Alternative sensor positions Sensors may be found in the roof (near the interior light unit, or may be installed within it), doors, kick panels, rear compartment fresh air intake duct and vent exits etc The sensors operate as described and are useful in that more control over temperature distribution throughout the vehicle can be achieved The ECU (electronic control unit) collects information from all the sensors described above and will use it to set the system to the most appropriate setting as determined by the drivers requirements Control of the dampers (flaps) can be either by vacuum actuators or stepper motors Airflow control Air volume and temperature control Coils Components An example of a stepper motor (servo motor) Stators Rotor Connected to flaps Temperature control and air distribution flaps are normally controlled by stepper motors but may be controlled by vacuum activated valves The stepper motor (servo motor) can be stopped at specific points in its armature rotation It allows the ECU to make very accurate and fine adjustments of output or movement, to an accuracy of 0.1 percent approximately The direction of rotation of the motors is determined by the relative phase of the pulses The stepper motor shown is a fixed speed DC motor which runs in forward or reverse to move the flap between fresh air and re-circulation positions - 85 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue The stepper motor consists of stators, slip rings, coils and a rotor, which contains permanent magnets The rotor moves one pole for every step e.g each time the coils are energised Coils energised ECU controls which coils are energised ECU Rotor Rotor stops at energised coils Coils off Servo or stepper motor can be stopped in an exact position the computer energises specific coils to attract the armature and stop it in the desired position In this example four coils have been used to maintain clarity When a new stepper motor is fitted it is essential that the end position and step angle are adjusted Calibration should be carried out with the engine running to obtain the correct running voltage - 86 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Damper operation (flaps) Water valve control cable Air inlet control cable Control panel Air mix control cable Air flow control cable There are two types of operating methods, a manual or lever and a digital (push button) type In the lever type, no electric motors are used The driver operates the controls manually and the cables move the flaps as the levers are moved Push button type Air inlet selector switches Air flow selector switches Pressing the buttons on the control panel causes the servomotors to operate the damper - 87 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Air inlet control servo motor (stepper) Air flow control servo motor (stepper) Servomotors are activated by the control unit (ECU) according to the selected temperature and airflow into the vehicle The motor changes the mixing of the warm air via the temperature damper in such a manner that the in-car temperature remains almost constant under all driving conditions Blower motor (interior fan) speed Variable speed blower (transistor control type) Heater unit Blower control unit The main blower motor is controlled by a power transistor (May be controlled by passing current through different resistance values also) The current flow through it is varied by the ECU the blower motor speed is therefore variable The speed is selected automatically when the system is in the AUTO mode and also if the driver selects the speed using the control panel The speed may be set using push buttons or a rotary control knob Note: When HI or LO is selected the motor runs continuously at maximum speed A feedback signal from the motor armature allows the ECU to monitor the speed of the motor and therefore the amount of ventilation being provided - 88 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Progress check Answer the following questions: List three types of sensors and three actuator control devices: Explain the meaning of NTC and PTC: An ambient temperature sensor measures what? Servomotors operate what? What controls servo motor operation? - 89 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Name two methods of controlling damper movement: Two types of damper are: Two methods of controlling blower speed are: The function of the air inlet damper is to: 10 The function of the air flow control damper is to: - 90 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Defroster A C Foot Rear B D E Side vent Centre vent Side vent The following should be answered by referring to the diagram above: a) The air flow mode control lever was set the defrost position but the front windscreen is still misty while warm air is being directed to the floor Name the malfunctioning damper(s): b) With the air flow control set to face, no air is coming from the centre vent Name the components that are not functioning: c) The air flow control lever is set to the foot position but warm air is not being directed to the floor (the temperature control lever and linked dampers are functioning normally) Name the malfunctioning damper(s): - 91 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Progress check Answer the following questions: State the main functional requirements of a vehicle heater system: What are the four main functions of air conditioning? What name is given to signal devices used in vehicle climate control systems? State the purpose of the filter fitted in the intake air flow passage of climate control systems: Explain the purpose of the AUTO air distribution control function: - 92 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue ... All Right Reserved LV35: Cooling Systems (3) Issue Name the parts from to 5: a d b c 3 - 16 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Describe... - 34 Copyright © Automotive Skills Limited 2003 All Right Reserved LV35: Cooling Systems (3) Issue Low cooling load When the cooling load is low, the pressure of the refrigerant vapour is low... Reserved LV35: Cooling Systems (3) Issue Servicing and Repair It is not possible to interchange hoses for R12 and R134a air conditioning systems Discharge and suction hoses for R134a systems use