Komatsu PC200-8M0 Shop Manual page 1170

SEN06151-00
Functions of major components
a For details of the numbers in the following sen-
tence, see "Air conditioner unit".
Evaporator
q Evaporator (1) is cooled by the low-pressure,
low-temperature refrigerant gas being sent from
expansion valve (3).
q Air from blower motor (4) is cooled and dehumid-
ified when passing through the fins of the evap-
orator (1).
Heater core
q Heater core (2) is warmed by the hot water (en-
gine coolant) being sent from the engine.
q Air from blower motor (4) is warmed when pass-
ing through the fins of the heater core (2).
Evaporator temperature sensor
q Evaporator temperature sensor (14) is installed
on evaporator (1) with the holder. Its resistance
changes in response to the temperature change
of the evaporator (1).
q The air conditioner controller determines the
evaporator temperature from the voltage value
of the evaporator temperature sensor (14) and
turns the compressor on/off to prevent freeze of
the evaporator (1).
Servomotors
a Servomotors are used to adjust the temperature
(air mix) and to perform vent (mode) change-
over.
q Whenever a switch on the machine monitor is
operated, the air conditioner controller delivers
power to the servomotor by raising the voltage
between terminals (6) and (7) to 24 V. (The rota-
tion direction changes based on the supply po-
larity.)
The servomotor contains a variable resistance,
q
and its resistance value changes as the motor
turns.
q The air conditioner controller delivers voltage at
5 V to the variable resistance and detects motor
rotation angle based on the potential difference.
12
80-100
When the door (damper) reaches the position
q
specified by each switch, the air conditioner con-
troller stops the supply of current to the servomo-
tor, then the corresponding door stops.
q When the potential difference fails to reach a
predefined voltage for control of the servomotor,
the air conditioner controller notifies the machine
monitor of an abnormality. [879EMC] or
[879FMC] is displayed in the "Electrical System"
(electrical systems abnormality record) screen in
service mode 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.
a When attempting to operate a servomotor during
inspecting, do not supply power directly between
servomotor terminals (6) and (7).
PC200, 200LC, 220, 220LC-8M0
100 Air conditioner
Air conditioner unit