FATC 16 B. LINEAR POWER MODULE (LPM) In case of FATC, a LPM is used to enable the ECU to control the blower speed in smaller increments. It is mounted on evaporator housing. C. 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 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 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. D. HEATER COIL Electric heater (PTC heater) is used in the HVAC. It is high voltage heater and directly connected to power distribution unit. Depending on temperature requirements, heater gets ON and It gets heated up. When air from HVAC blower is passed through heater, hot air comes out from HVAC outlet. As soon as cabin temperature requirement is met, heater gets off. Request from FATC panel goes VCU to switch ON / OFF of PTC heater. Actual operation of PTC heater happens through VCU.
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