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17

When the indoor unit turns on the power for the outdoor unit, the outdoor control circuit power supply of 5V is
generated, and the CPU begins operation. In order to ensure that the CPU always starts in the same mode, a LOW
input must be input to the CPU reset port for a fixed time interval. The reset circuit performs this function.

When 5V is applied to the control circuit, the oscillation circuit begins operation, starting the CPU. When this oscillator
stabilizes, LOW input is asserted at the CPU reset port 11 for a fixed time interval, starting the program and initializing

When the power for the outdoor unit is turned on, it outputs LOW to CPU IC1 pins 20 and 21, setting photocoupler PC2
to ON, to allow it to receive serial signals from the indoor unit. When PC2 goes ON, the serial signal passes through the
VA cable and operates PC1 via the indoor unit control. When PC1 goes ON, HIGH is input to CPU IC1 pin 19; when it
goes OFF, LOW is input. The CPU reads the HIGH/LOW operation and generates the various corresponding outputs. If
it is able to read correctly, it invert the LED; if it is not able to read correctly, it turns on the LED.

If the outdoor unit reads the serial signal from the indoor unit correctly, the outdoor unit next sends back a serial signal
by setting CPU IC1 pins 20 and 21 to LOW/HIGH to turn ON/OFF photocoupler PC2. During this time, the indoor unit
waits for a signal from the outdoor unit by applying a continuous voltage between (N) and (2).

It is possible for 220/240 V AC to be applied to terminal board (N)-(2) because of an error in the wiring connections
between the units. In order to prevent damage to the unit in the event of such an error, a high voltage resistant
photocoupler is used for PC2.

+

C25

5V

–

CPU (IC1) pin 11

IC3

C35

Blue

Red

R20

R41

R43

R42

R44 R45

C34

R18

R19

R16

D6

(N)

PC2

PC1

5V

(2)

CPU (IC1)
pin 19

CPU (IC1)
pin 20 and 21

Terminal
Block

C36

18

Because a large current is needed to drive a relay, it cannot be driven directly by the CPU. The signal from the CPU is
received by the digital transistor Q2, which is then used to drive the relay. When CPU IC1 pin 22 is set to HIGH output,
Q2 goes ON, and the current flows from the 13V through the primary side of RY1 to GND, and RY1 goes ON. When
RY1 goes ON, 220/240 V AC is asserted at the outdoor fan motor and the outdoor fan begins to turn.

CNR1 is connected to absorb the relay contact noise.

CPU (IC1) pin 22

FAN MOTOR

Noise

filter

circuit

C11

Q2

RY1

CNR1

CN3

D4

13V

N

1

Terminal
Block

19

The rotary four-way valve operates when a DC voltage is applied. When the current flows in the (a) direction shown in
the diagram above, the air conditioner is a heater, when the current flows in the (b) direction, it is a cooler. Power flows
in the rotary four-way valve for 1.5 seconds, and only flows just before the compressor is activated.

When activating the cooling operation, CPU IC1 pin 25 is LOW output and Q4 is OFF, so RY3 is on the D7 side. In this
state, if CPU IC1 pin 26 is set to HIGH output, Q3 goes ON, RY2 goes ON, and a half-wave rectification current flows in
the (b) direction, operating the four-way valve in the cooling mode.

When activating the heating operation, CPU IC1 pin 25 is set to HIGH output, Q4 goes ON and RY3 goes to the D8
side. By setting CPU IC1 pin 26 to HIGH output, Q3 and RY2 go ON. In this way, when RY2 is set to ON, the half-wave
rectification current flows in the (a) direction, and the four-way valve operates in the heating mode.

Both Q3 and Q4 are digital transistors and, like the outdoor fan drive circuit, are used to drive the relay.

CNR2 is connected to absorb the relay contact noise.

CPU (IC1) pin 26

CPU (IC1) pin 25

Noise

filter

circuit

Q4

13V

CNR2

CN4

N

1

Terminal
Block

Q3

D5

RY2

RY3

D10

D7

D8

Four-way
valve coil

a

b

20

When 220/240 V AC is supplied to terminal boards (1) and (N), an AC power supply rush current will flow temporarily
because there is an uncharged electrolytic capacitor on the load side. A current surge suppression circuit is included to
prevent damage to the circuit from this rush current,

When 220/240 V AC is supplied between terminal boards (1) and (N), the AC current passes through posistor PTC1 to
charge the electrolytic capacitor on the load side. The rush current is suppressed by passing it through the posistor.
When the load is charged on the electrolytic capacitor, CPU IC1 begins operation, and after an approximately 0.5
second delay, pin 23 goes to HIGH output. When pin 23 goes HIGH, digital transistor Q1 goes ON, MRY1 (main relay)
goes ON, and the circuit begins to operate normally.

Digital transistor Q1 is used here because, like the outdoor fan relay, the CPU cannot directly drive the relay.

CPU (IC1) pin 23

Noise

filter

circuit

13V

N

1

Terminal
Block

Load

Q1

MRY1

PTC1

D3