General Assist Technical Reference

Four Way Valve (4WV) Explanation

Reversing valve operation, AC and DC solenoid types
Technical reference for heating/cooling changeover and 4-way valve diagnosis
The 4-way valve (4WV), also known as the reversing valve, changes the direction of refrigerant flow so the air conditioner can operate in either heating or cooling.

1. Four Way Valve Operation

The 4-way valve changes position according to whether the system is operating in heating or cooling.

Operating Mode4-Way Valve State
HeatingON / Energised
CoolingOFF / De-energised
Standard operation: On the systems referenced, the reversing valve is energised during the heating cycle and de-energised during the cooling cycle.

2. AC 240 V Reversing Valve Solenoid

Fujitsu outdoor units traditionally use approximately AC 240 V to energise the reversing / 4-way valve solenoid during heating operation.

AC Solenoid Operation
HeatingApproximately 240 VAC supplied to the solenoid
CoolingSolenoid supply OFF
Typical Solenoid Cable ColoursBlack / Blue

3. DC Pulse Reversing Valve

Some newer models use a DC pulse-operated 4-way valve rather than a continuously energised AC solenoid.

The reference identifies the following models:

9KMTC / 12KMTC / 18KMTC / 22KMTC / 24KMTC

On these models, DC power is supplied only while the reversing valve is changing over.

Important difference: A DC pulse-type valve does not require continuous voltage to remain in position. Once moved, the valve can remain in either state without power.

How the DC valve holds position

The DC-powered 4-way valve uses a magnet in the reversing valve solenoid. This allows the valve to remain in its selected position even after the DC pulse has been removed.

This means that when checking a DC pulse-operated system, the absence of continuous voltage at the solenoid does not automatically indicate a fault.

DC solenoid wiring

Typical DC solenoid cable colours: Red / Blue

The DC operating voltage can be measured at the PCB where the reversing valve receives its supply.

4. Diagnostic Approach

1Confirm whether the system uses an AC 240 V solenoid or a DC pulse solenoid.
2Confirm the unit operating mode: heating or cooling.
3For an AC solenoid, check for approximately 240 VAC during heating.
4For a DC pulse solenoid, monitor voltage during the actual changeover event, not simply while the system is already operating.
5If voltage is being supplied correctly but the refrigerant circuit does not reverse, investigate the solenoid and mechanical 4-way valve operation.

5. AC vs DC Quick Reference

ItemAC SolenoidDC Pulse Solenoid
Supply TypeApproximately 240 VACDC pulse
HeatingSolenoid energisedPulse used to change valve position
Continuous Power RequiredYes, while energisedNo
Typical Wire ColoursBlack / BlueRed / Blue
Voltage TestCheck during heating operationCheck during changeover
Diagnostic caution: Do not diagnose a DC pulse-type 4-way valve as faulty simply because there is no voltage present after the system has completed its changeover. The valve is designed to remain in position without continuous power.
Electrical safety: Voltage testing should only be carried out by appropriately qualified personnel using suitable test equipment and safe electrical work practices.