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FATC
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ii. 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.
iii. 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.
iv. 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 heat-
er, 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.