Automotive Air Conditioning System Evaporator om Hen resi, ad Lo prs ie a Low presse st one ME 467 : Automobile Engineering Dr. Md, Ehsan © 2015 ME, BUETAutomotive Air Conditioner: The automotive air conditioner is an accessory system that cleans, cools, dries, and circulates passenger-compartment air. This may also provide some indirect noise control. The air conditioner is basically a mobile refrigeration system. It includes an air-delivery system and a temperature-control system. The parts are connected by wiring, hoses, and tubing. The compressor in the automotive air conditioner is powered by the engine. Running the air conditioner may result in reduced engine performance and fuel economy. In a vehicle with factory-installed air conditioning, the heater and air conditioner are integrated into a heater-air- conditioner. The automotive air conditioning system high pressure circuit consists of the - Compressor, Condenser and Receiver-Drier; while the low pressure part of the circuit consists of ~ the Thermal Expansion Valve and the Evaporator. The unit may be manually-controlled or automatically-controlled. In manually controlled ones the driver selects the desired mode by moving a mode or selector lever. Its position shuts off or allows air delivery through the vents, and controls heater and air-conditioner operation. Moving the temperature lever on the control panel controls the temperature of the air entering the passenger compartment. Turning the blower switch or fan control determines the speed of the blower motor. The automatic system is basically the same but allows the driver to select automatic control and the desired temperature. The system will then maintain that temperature by providing heat or cooling as required. Many systems also automatically adjust the blower speed. The instrument-panel controls usually allow the driver to override the automatic operation. VENTILATING THE PASSENGER COMPARTMENT For health and comfort, some fresh air must pass through the passenger compartment. This replaces the stale and sometimes smoke-flled air inside the vehicle. The process is called ventilation. There are two methods: uncontrolled ventilation and controlled ventilation. Uncontrolled ventilation occurs when windows are opened. Controlled ventilation is either ram-air or Power. In the ram-air system, opening vents or ducts admits air to the passenger compartment. Forward movement then forces or rams air into the vehicle. However, when the vehicle stops or moves slowly, little fresh air enters. This is one reason most vehicles have a power ventilating system. An electric blower motor and fan provide air circulation regardless of vehicle speed. The blower is also part of the heater and the air conditioner. It is important that the cols air from the air conditioning outlets are well circulated all over the vehicle. The passengers can choose to have fresh air in the car or use recirculation of the alr inside the ME 467 : Automobile Engineering Dr. Md, Ehsan © 2015 ME, BUETpassenger cabin. Switches can be used to direct the air flow to particular set of vents/outlets for comfort. The speed of the blowers can also be changed to regulate the air circulation rates. Although the cool air is supplied by the blower passing air across the evaporator section of the air conditioner, hot air is supplied by the blower passing air across a heater core which uses hot coolant engaged in engine cooling as the heat source. In some vehicle the hot air flow is supplemented by an electric heater attached to the heating core to supply hot air, while the engine is still cold hhot water valve heater hoses ‘accumulator, heater core water pump. ‘AC/heating control module condenser AUXILIARY REAR HEATING AND COOLING ‘Some vehicles have a large interior space to heat and cool (eg. microbus, minibus). These vehicles may have an auxiliary rear heating-and-cooling system. It keeps the rear passengers more comfortable without disturbing air distribution to the front seat, The auxiliary system may be in the trunk of a car. It may be on the roof or in one side of a van. The system may include a heater core, evaporator core, orifice tube or expansion valve, blower motor and controls, and ducts. The auxiliary system does not have its own compressor or condenser. Hose and tubing carry the refrigerant between the front of the vehicle and the rear evaporator. Hot engine coolant is also piped to and from the rear heater core. ME 467 : Automobile Engineering Dr. Md, Ehsan © 2015 ME, BUETComponents of Automotive AC Panel ME 467 : Automobile Engineering Dr. Md, Ehsan © 2015 ME, BUETCompressor: The compressor is a pump driven by a belt attached to the engine's crankshaft When the refrigerant is drawn into the compressor, it is in a low-pressure gaseous form. Once the gas is inside the pump, the compressor ves up to its name. The belt drives the pump, which puts the gas under pressure and forces it out to the condenser. Compressors cannot compress liquids, only gasses. Compressors can be fixed displacement or variable displacement(wobble/swash plate) types. COMPRESSOR CLUTCH The compressor clutch is @ solencid-type magnetic clutch located in the compressor pulley. The clutch engages and disengages so the compressor shaft turns only as needed. When the clutch engages, the compressor runs and cooling takes places. When compressor operation is not needed, the clutch disengages. Then only the pulley turns. The pulley is driven by a belt from the engine crankshaft. The clutch has a stationary coll that becomes magnetized when voltage is applied. A clutch hud or armature attaches to the compressor shaft. When no voltage is applied to the coil, the armature moves forward slightly. This disengages the compressor by opening a slight air gap between the armature and the front face of the pulley. The pulley mounts on ball bearings so it can rotate freely when the Clutch is disengaged. Applying voltage magnetizes the coil. This pulls the armature back and locks the pulley to the armature, Now the compressor shaft rotates with the pulley. ME 467 : Automobile Engineering Dr. Md, Ehsan © 2015 ME, BUETCYCLING AND NON-CYCLING COMPRE ORS: Many automotive air conditioners have a compressor with a cycling clutch. It automatically engages and disengages to cycle the compressor on and off. This regulates the temperature of the conditioned air. Clutch cycling is often controlled typically by evaporator temperature or pressure, sensed by an electric switch. ‘Some compressors run continuously while the engine is running and the air conditioner is ON. These compressors have a non-cycling clutch. Such systems often have a variable-displacement compressor. It runs continuously and varies the amount of refrigerant pumped according to need. Expansion Valve Air Conditioning System Orifice Tube Air Conditioning System ees warm uaa Ho enpeeGan am et Condenser: The condenser is basically a heat exchanger with lot of surface area, and it serves the same purpose as the one in your car: to radiate heat out of the system, The refrigerant enters the condenser as a pressurized gas from the compressor. The process of pressurizing the gas and moving it to the condenser creates heat, but air flowing around the twisting tubes of the condenser cool the refrigerant down unti it forms a liquid again. The liquid refrigerant is now a high-pressure liquid and nearly ready to cool the car. This is typically located at the most front end of the car, parallel to the engine coolant radiator, to get the assistance of incoming air when the car runs forward. ME 467 : Automobile Engineering Dr. Md, Ehsan © 2015 ME, BUET