Hitachi RAC-25JX4, Service Manual

Page: 51 / 119

Ð 56 Ð
8. Ventilation Fan Motor Circuit
Microcomputer
VENTILATION
DIFECTION
VENTILATION
FAN OUTPUT
44
40
0V
C935
R934
5V
R933
C932
C933
R935
K-12V
CN11
1
2
3
4
M
0V
0V
T1
T2
CN11 pin
Voltage waveform
③
T1: Low-speed rotation
T2: High-speed rotation
Convert to analog voltage at the ventilation
fan motor internal circuit.
When T2
When T1
Fig. 8-2
Fig. 8-1
Ventilation fan motor is a 12V DC motor. It operates by inputting DC12V power (K-12V) and ventilation fan PWM signal to
CN11
pin and CN11 pin respectively and outputting ventilation abnormality detection signal from CN11 pin.
(K-12V) is generated from DC-DC converter of the ventilation fan motor circuit. It is the power source exclusively for the
ventilation fan motor and is independent from 12V of the power circuit for control.
Ventilation fan PWM signal (Microcomputer
pin) is a command instruction to the ventilation fan motor. This signal is
converted into analog voltage inside the ventilation fan motor to operate it.
If width of PWM signal is made wider, analog voltage becomes higher and the motor rotation speed becomes faster, as
shown in Fig. 8-2.
When the motor is rotating normally, the ventilation abnormality detection signal is Lo (approximately 0V). In the event that
the fan is locked or unable to rotate due to failure, ÒHiÓ ventilation abnormality detection signal (approximately 5V) is output
(Microcomputer
pin) to show abnormality.
When the Microcomputer receives this signal, it suspends ventilation fan PWM signal and outputs the same signal again
after 30 seconds have elapsed. If the abnormality continues and retry is repeated 5 times within 3 minutes since the first
abnormality detection, abnormality is judged and two way air exchange lamp blinks (lit for 4 seconds and off for 1 second).
① ③ ④