HVAC 10 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 dehumidification 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 monitors 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).
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