Komatsu PC88MR-10 Shop Manual page 1336

80 Appendix
Air conditioner unit
Automatic mode of air conditioner
Inside air temperature sensor (13) detects the temperature inside operator's cab based on changes in
resistance. The air conditioner controller converts the change in resistance of inside air temperature
sensor (13) into the change in voltage to determine the room temperature.
The air conditioner controller checks the voltage of inside air temperature sensor (13) and controls the
room temperature so that it matches the setting made on the machine monitor.
The air conditioner controller also takes into consideration data from the sunlight sensor and the outer
sensor (outside air temperature sensor) when adjusting the room temperature.
Functions of major components
a For details of the numbers in the following sentence, see Air conditioner unit .
Evaporator
(ALL-K549-042-K-00-A)
Evaporator (1) is cooled by the low-pressure, low-temperature refrigerant gas being sent from expansion
valve (3).
Air from blower motor (4) is cooled and dehumidified when passing through the evaporator fins.
Heater core
(ALL-K547-042-K-00-A)
Heater core (2) is warmed by the hot water (engine coolant) being sent from the engine. Air from blower
motor (4) is warmed when passing through fins of the heater core (2).
Evaporator temperature sensor
Evaporator temperature sensor (12) is installed to evaporator (1) with the holder. Its resistance changes in
accordance with the temperature change of the evaporator. The air conditioner controller determines the
temperature of evaporator (1) from voltage changes of evaporator temperature sensor (12) to prevent
freeze of the evaporator.
Servomotor
(ALL-K5D2-042-K-00-A)
a Servomotors are used to adjust the temperature (air mix) and to perform vent (mode) changeover.
When a switch on the machine monitor is operated, the air conditioner controller applies 24V power
between servomotor terminal B (6) and servomotor terminal A (7). (Rotation direction switches according
to the polarity of supply voltage.) )
The servomotor contains a variable resistor, and its resistance value changes as the motor rotates.
The air conditioner controller applies a voltage of 5 V to the variable resistor and determines the motor
rotation angle from the potential difference.
When the door (damper) reaches the position specified by each switch, the air conditioner controller stops
the supply of current to the servomotor, then the corresponding door stops.
When the air conditioner controller cannot recognize the potential difference that corresponds to the
command to the servomotor, it generates a air conditioner failure code to inform the machine monitor of
failure in air conditioner system. Failure code [879EMC] or [879FMC] is displayed on the electrical system
failure record screen of the machine monitor.
a FRESH/RECIRC air changeover servo motor does not feature a variable resistance, and therefore,
does not have a self-diagnosis function.
80-12
(ALL-K540-001-K-00-A)
(PC138-K5FF-042-K-00-A)
PC88MR-10