Hitachi RAS-25CNH2 Service Manual page 36

7. Temporary Switch
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.
8. DC Fan Motor Drive Circuit
Fig. 8-1 shows the indoor DC fan motor drive circuit.
G
Micro computer
R920
Fan PMW output 57
Output divider
8
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.
Q903 is switched on and off according to the signal at fan PWM output pin
G
is smoothed by D901, L901 and C901 to drive the fan motor.
The output voltage is divided by R901 and R903 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`R915 and input to fan current
G
9
detection pin
corresponding to the fan rotation speed.
SW701
J
35V
Q903 L901
D901
0V
I
0V
5V
C933
R931
R932
R930
0V
C940
D902
0V 0V
. Microcomputer detects overcurrent comparing it with the current judgment value
R709 R710
C701 ZD701
0V 0V
0V
Fig. 7-1
Fig. 7-1
5V
C901 R901
C942
R903
0V
0V
Fig. 8-1
Fig. 8.1
– 39 –
12V
37 X1
MICRO COMPUTER
RED
5
4
YEL
3
2
BLU
1
CN10
0V
Terminal board D
J
to control the voltage which
M
Indoor DC
Fan motor
8
; the micro