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HVAC
15
ELECTRICAL CONTROL UNIT
The Control Panel is also the HVAC control unit. In
addition to the functions of a control panel it controls
2 additional operations mentioned below:
A. DEFROST
Whenever the HVAC is put in leg-defrost or Defrost
mode the control unit switches ON the compressor to
operate in normal AC mode to ensure dehumidifica-
tion of incoming air and switches the air inlet valve to
fresh air mode. This is done in order to avoid sudden
fog formation (flash fogging) on the windshield. This
logic can be manually overridden.
B. ECON MODE
When in Econ
(Economy)
mode the compressor
cuts-off at a higher evaporator temperature than in
normal AC. This results in less fuel being consumed
by the engine since the compressor is cut off at
higher temperature.
In addition to these logics the control unit also moni-
tors the evaporator temperature through thermister
and shuts the compressor OFF if the temperature is
much below the permissible limits.
C. REAR DEFOGGER /ORVM DEFOG
When the rear defog switch is pressed the control
unit switches on the heater grids on the rear window
to clear them of the fog.
When the button is pressed first time it turns on the
heater grid for approx 15 mins and switches it off.
TRINARY PRESSURE SWITCH
The pressure in the system is monitored by a Trinary
pressure switch. The Trinary pressure switch triggers
at 3 pressure values and sends request to Engine
EMS ECU for compressor shut OFF or to increase
radiator fan speed depending on system pressure.
(For details refer HVAC components section).