HVAC 13 7. HVAC UNIT COMPONENTS The front HVAC unit in vehicle comprises of the following parts: A. BLOWER. B. EVAPORATOR COIL AND TXV (THERMAL EXPANSION VALVE) C. HEATER COIL A. BLOWER:- The Blower is located at the top on the backside of HVAC unit when viewed from inside the vehicle. It acts as a centrifugal pump drawing in air from the center and pushing it out diagonally. The air flows through the evaporator and the heater coil and then to the cabin. The Blower speed is controlled using a blower control module. Blower Motor Specification MAKE GBM S SERIES VOLTAGE DC 12.5 V CURRENT 21.6 A MAX RATING TORQUE 0.45 Nm RATING SPEED 3300 ± 200 rpm RATING OUTPUT - AIR FLOW 416 M3/HR CLAMPING TORQUE TBD Nm B. EVAPORATOR COIL AND TXV (THERMAL EXPANSION VALVE) EVAPORATOR COIL It is a heat exchanger cum dehumidifier which absorbs heat and moisture of the air passing through it to give cold dehumidified air. As the refrigerant absorbs the heat it changes its state from liquid to vapors. A thermistor (temperature sensor) is used to measure the temperature of the air passing over the evaporator in order to avoid freezing. TXV (THERMAL EXPANSION VALVE) The TXV used is block type valve. It consists of a two passages one for refrigerant flowing into the evaporator and the other for refrigerant coming out of evaporator and into the compressor. A temperature sensing element is placed in the outlet passage. This sensing element is filled with a fluid which expands and contracts when there is rise or fall in the temperature. When the temperature of the refrigerant flowing out of the evaporator rises it causes the expansion of the refrigerant in the sensing element which in turn pushes the pin, such that the ball valve blocking the orifice opens to allow more refrigerant into the evaporator. The pressure spring provided below the ball tends to close the ball valve and hence this pressure has to be overcome in order to open the valve. There is a passage in the block valve where refrigerant flowing out can build pressure under a diaphragm on which the sensing element is mounted causing the diaphragm to move up; this provides the needed pressure correction while regulating the refrigerant into the evaporator. C. HEATER COIL A heater coil is a radiator-like device used in heating the cabin of a vehicle. Hot coolant from the vehicle's
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