SAFARI BSVI SERVICE MANUAL

HVAC 23 iii) EVAPORATOR COIL AND TXV (THERMAL EXPANSION VALVE) EVAPORATOR COIL It is a heat exchanger cum dehumidifier which ab- sorbs heat and moisture of the air passing through it to give cold dehumidified air. As the refrigerant ab- sorbs the heat it changes its state from liquid to vapour. 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 temper- ature. When the temperature of the refrigerant flowing out of the evaporator rises it causes the ex- pansion 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 refriger- ant 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 re- frigerant into the evaporator. iv) HEATER COIL A heater coil is a radiator-like device used in heating the cabin of a vehicle. Hot coolant from the vehicle's engine is passed through a winding tube of the core, a heat exchanger between coolant and cabin air. Fins attached to the core tubes serve to increase surface for heat transfer to air that is forced past them, by a fan, thereby heating the passenger com- partment.