HARRIER SERVICE MANUAL PART -1

HVAC 11 5. HVAC SYSTEM LAYOUT AND WORKING WORKING The HVAC system is similar to a conventional auto- motive HVAC system. It consists of a Compressor, a Condenser, and an evaporator. System wise it can be divided as low pressure side and the high pres- sure side, which is divided at the expansion valve. REFRIGERANT CYCLE The compressor compresses the refrigerant R134a, increasing its pressure and temperature. This high pressure hot vapour is then made to pass through the condenser (condenser is cooled by the passing ambient air), where it gives its latent heat to turn to liquid, the drop in temperature is small, as most of the heat lost will be latent heat resulting in change of state to liquid. This liquid is made to pass through a receiver drier, which is used to filter out the moisture and also al- lows only liquid to flow further to the Thermal Expansion Valve (TXV valve). The high pressure low temperature liquid then expands in the expansion Valve where the refrigerant pressure drops consid- erably, which also results in a drop of temperature. This cold low pressure liquid is circulated through the evaporator coil, where it absorbs the heat of the am- bient air made to pass through it by forced circulation of the blower. The liquid refrigerant absorbs the la- tent heat required to change to vapour state and turns to vapour. There is no considerable change in temperature as the heat absorbed by the refrigerant is only latent heat. This vapour then flows to the compressor and the cycle continues. ENGINE COOLANT FLOW A small amount of hot coolant from the engine is made to pass through the heater coil keeping it at a higher temperature all the time. From the heater coil the coolant flows to the water pump and is again circulated through the Engine. AIR FLOW The air is drawn in through the inlet duct due to the suction created by the blower. The blower forces either the ambient air or the cabin air depending on the mode selected (Fresh Air mode or Recirculation mode) to flow over the evaporator which lowers the temperature of the ambient air. The incoming air also gets dehumidified as the moisture condenses when the air flows over the cold evaporator fins. This cold dehumidified air is then mixed with the hot air ( if re- quired) to attain the temperature selected by the occupant; the mixing control is done by the heater door opening.