Komatsu PC88MR-10 Shop Manual page 1335

A: Refrigerant inlet (from condenser)
B: Refrigerant outlet (to compressor)
C: Hot water inlet
D: Hot water outlet
1. Evaporator
2. Heater core
3. Expansion valve
4. Blower fan and blower motor
5. Air mix servomotor
6. Air mix door
7. Vent (mode) changeover servomotor
8. Mode changeover door
9. FRESH/RECIRC air changeover servomotor
10. FRESH/RECIRC air changeover servomotor
11. Power transistor
12. Evaporator temperature sensor
13. Inner sensor (inside air temperature sensor)
14. Recirculation air filter
a "Doors" are sometimes called "dampers".
Function
(PC88MR-K540-042-K-00-A)
The air conditioner unit consists of evaporator (1) and heater core (2), and is used to cool down or warm
up the air in the cab.
Temperature control
When the temperature control switch on the machine monitor is operated, the set temperature data is sent
to the air conditioner controller that is located at the rear of the operator's seat. The air conditioner
controller controls air mix servomotor (5) to change the angle of air mix door (6) so that the set
temperature is reached
Over-cooling (Freezing) prevention
Evaporator temperature sensor (12) varies the resistance of its resistor according to temperature.
The air conditioner controller converts the change in resistance of evaporator temperature sensor (12) into
the change in voltage to determine the temperature of evaporator (1).
The air conditioner controller performs control to prevent freezing of the evaporator (1) by operating the
compressor clutch relay (*) to stop the compressor.
*: See "Testing relays" for details regarding the compressor clutch relay.
Air flow adjustment
When the air flow adjusting switch on the machine monitor is operated, the set air flow data is sent to the
air conditioner controller. The air conditioner controller controls blower motor (4) by using power transistor
(11) in order to adjust the air flow.
Vent (mode) changeover
When a vent selector switch on the machine monitor is operated, mode data is sent to the air conditioner
controller. The air conditioner controller controls vent (mode) changeover servomotor (7) to adjust the
opening and closing angles of mode changeover doors so that the selected vents are available.
FRESH/RECIRC air changeover
When the FRESH/RECIRC air selector switch on the machine monitor is operated, the set data of
FRESH/RECIRC air changeover is sent to the air conditioner controller. The air conditioner controller
controls FRESH/RECIRC air changeover servomotor (9) to open or close FRESH/RECIRC air
changeover door (10).
PC88MR-10
80 Appendix
Air conditioner unit
80-11