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HVAC
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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.
PINOUT
PIN NO
DESCRIPTION
1
CONTROL
2
DIAGNOSTICS
3
- MOTOR
4
+ BAT
5
GND
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 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.