Hitachi RAS-07G4 Service Manual page 50

10. Temporary Switch
The temporary switch is used to operate the air conditoner temporarily when the wireless remote control
G
is lost or faulty.
The air conditioner operates in the previous mode at the previously set temperature. However, when the
G
power switch is set to OFF, it starts automatic operation.
11. DC Fan Motor Drive Circuit
Fig. 11-1 shows the indoor DC fan motor drive circuit.
G
MICRO COMPUTER
(AX-3U)
FAN PWM
57
OUTPUT
FAN PWM
8
FEEDBACK
FAN CURRENT
9
DETECTION
The circuit produces the fan motor drive voltages, 8-33V, from 35V DC supplied from the outdoor unit and
G
controls the fan motor speed.
Q901 is switched on and off according to the signal at fan PWM output pin
G
is smoothed by D902, L901 and C901 to drive the fan motor.
The output voltage is divided by R919 and R920 and is input to divided voltage output pin
G
computer controls the fan PWM output so the output voltage is set to the specified value. The chopper
frequency of the fan PWM output is 15.7kHz.
In the Fan current detection circuit, 35V line current is detected by R906 and input to fan current detection
G
9
pin . Microcomputer detects overcurrent comparing it with the current judgment value corresponding to
the fan rotation speed.
TEMPORARY SWITCH
SW1
D901 R912
R916
I
0V
R931
R932
C932
D904
0V 0V
R609
0V
Fig. 10-1
J
L901
D902 C901 R919
R920
0V
0V
0V
5V
R930
Fig. 11-1
– 55 –
5V
TELECON
31
(AX-3U)
MICRO COMPUTER
RED
5
5V
4
YEL
3
C942 2
BLU
1
CN10
0V
3
CN3M PIN NO.
J
to control the voltage which
M
Indoor DC
Fan motor
8
; the micro