Hitachi RAC-18SX8 Service Manual page 163

6. Control circuit of the DC fan motor
・This model incorporates a fan motor control circuit in its outdoor electrical installation.
Outdoor electrical installation
Smoothing capacitor ( 2A fuse )
Switching power supply
The DC fan motor of this model is controlled by using the outdoor microcomputer according to operation commands from the
indoor microcomputer.
To match the motor speed to these operation commands, the product estimates the real rotation speed based on the DC
current flowing through R746 and controls the rotation speed.
This DC current is used to detect any overcurrent and other fan motor failures.
(1) Fan motor control at startup
When the fan is turning at operation startup due to a strong wind or other disturbance, the product will change in behavior
as follows according to the direction and rotation speed.
A forward wind is defined by the direction the wind blows out of the mouth ring.
When there is a strong reverse wind: To protect the equipment, this product will not perform control. The fan will turn in
When there is a reverse wind: After the wind slows down gradually and stops, the product will control its rotation speed in
When there is a forward wind: The rotation speed is controlled as it is.
When there is a strong forward wind: To protect the equipment, the product will not perform control. The fan will then turn
(2) Fan motor control during operation
The fan speed may go down due to a strong wind or other disturbance while the fan motor is running. When this state has
continued for a long time, the fan will stop. (The self-diagnosis lamp LD301 will blink 11 times.) At startup, the product will
start again according to the control procedure specified in (1).
F4
＋ ＋
R746
DC current Id
reverse direction in response to the wind. As the wind weakens, the product will start
automatically.
forward direction.
in forward direction in response to the wind. As the wind weakens, it will start
automatically.
IPM2
Drive circuit
IP
Microcomputer
Fig. 6-1
– 196 –
VH5P lacking
CN24
White
1
W Red
2
3
U White
4
5
V Black
Fan motor