Hitachi RAS-25JX4 Service Manual page 74

0. Outdoor DC Fan Motor control circuit
This model uses DC Fan Motor which has a controller circuit built in the Motor.
This DC Fan Motor will rotate by control voltage apply to Vsp input. (Voltage range: 1.7 to 7V DC)
Vsp high : Faster ;
Vsp low : slower ;
Vsp lower than 1.7V : stop
Motor will output FG pulse by following this motor revolution.
Outdoor microcomputer will output PWM control signal from 75 by following the instruction from
indoor microcomputer.
This PWM control signal will convert to Vsp voltage by smoothing circuit (R242 & C209)
Fan motor will start to rotate when Vsp was proceeding over than 1.7V, and generate FG pulse by
rotation speed.
FG pulse will feed back to Outdoor microcomputer 15 .
DC Fan Motor circuit has to match the Fan Motor revolution with instructed revolution. Such as...
FG feedback: Faster Instruction: Slower ... Decrease pulse width
FG feedback: Slower Instruction: Faster ... Increase pulse width
FG pulse is also used for Fan Motor failure detection.
Microcomputer will monitor FG pulse 30 seconds after start the fan motor. If there is no signal detected,
it will consider that the Fan Motor was malfunction and stop the operation. In this case, LD302 on control
P.W.B. will blink 12 times. (Fan Motor lock detected)
R107 and IC4 are used for Fan Motor over current.
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