AIR CONDITIONING SYSTEM


  1. FUNCTION OF MAIN COMPONENTS

    Component Function
    Heater Assembly Improves heating performance at low temperatures.
    Power Heater Switch (Heater Switch Assembly) Pressing this switch operates the combustion type power heater.
    Fuel Pump Supplies fuel to the combustion type power heater.
    Glow Plug Ignites the fuel in the combustion type power heater.
    Engine Coolant Temperature Sensor Detects the temperature of the engine coolant in the heater.
    Flame Sensor Detects the temperature of the exhaust gas.
    Overheating Prevention Sensor Detects the temperature of the wall surface of the combustion chamber.

  2. SYSTEM CONTROL


    1. When the engine is operating, turning the power heater switch (heater switch assembly) on causes the air fan to operate for several seconds for verification purposes. Then, the glow plug starts to preheat the combustion chamber. After that, the fuel pump and air fan turn on in order to start low combustion. The fuel pump speed is then increased in steps. This is accompanied by a gradual increase in the speed of the air fan, thus leading to high combustion.

    2. When the ignition switch is turned off or the power heater switch (heater switch assembly) is turned off, the fuel pump stops, causing the combustion to stop. For the purpose of after-purge, current is applied again to the glow plug, and the air fan is activated for several seconds. Then, the entire system comes to a stop.

      A00XRH3E03

    3. While the system is operating, it controls the fuel pump speed and switches between high combustion and low combustion, constantly keeping the engine coolant temperature between 75°C (167°F) and 85°C (185°F). If the engine coolant temperature exceeds 85°C (185°F), the fuel pump stops automatically to stop combustion. Thereafter, when the engine coolant temperature reaches 75°C (167°F) or lower, combustion is started again. The operation of the glow plug, the air fan, and the fuel pump during extinguishing and re-igniting is the same as when these are operated by a switch as mentioned previously.

      A00XRC3E02

    4. For self-protection, the combustion type power heater stops if an abnormal condition is detected. Descriptions of the function are indicated below:

      Function Outline
      Dry Run Prevention If the temperature detected by the engine coolant temperature sensor or the overheating prevention sensor exceeds 125°C (257°F), the power heater ECU determines that the heater is operating without water and automatically stops the system.
      Overheating Prevention If the difference in temperature detected by the engine coolant temperature sensor and the overheating prevention sensor exceeds 25°C (45°F), the power heater ECU determines that the flow volume of the water is insufficient and automatically stops the system.
      Non-ignition or Misfiring Detection If the temperature of the exhaust gas detected by the flame sensor is low, the power heater ECU determines that a non-ignition or a misfiring condition exists and automatically stops the system.
      Open or Short Circuit Detection If an open or short circuit exists in the sensors or actuators, the power heater ECU automatically stops the system.
      Air Fan Seizure Detection If the air fan seizes, the power heater ECU automatically stops the system.

  3. DIAGNOSIS


    1. If a malfunction occurs in the combustion type power heater system, it is possible to access the DTC by using SST that has been designed exclusively for the combustion type power heater system. For details, refer to the Repair Manual.