HVAC (ETC) 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. 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. C. TRINARY PRESSURE SENSOR Trinary pressure sensor is provided on the high pressure tube liquid line of the refrigerant and it is functionally connected to engine EMS to control the AC compressor and radiator/ condenser fan through the Engine EMS. It also gives a feedback to the Control panel in case of its intervention. The operating pressure ranges for the Trinary pressure switch is as Pressure OFF ON DIFF Low 0.196±0.02 0.226+0.025 More than 0.02 Medium 1.47±0.15 1.96±0.12 ---------- High 3.14±0.2 (2.55) 0.59±0.2 Location The pressure switch is located on the high pressure refrigerant liquid tube on radial vertical support frame. -0.03
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