Learn how the 4-way reversing valve controls the heating and cooling process in air conditioners and heat pumps. See step-by-step working, refrigerant flow direction, and the complete heating/cooling cycle explained with a clear labeled diagram. Ideal for HVAC students, technicians, and beginners.
4 way valve working explain diagram
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AC 4 way valve (reverse valve) Electric Wiring 1st Diagram
AC 4 way valve (reverse valve) Electric Wiring 2nd Diagram
4 Way Reversing Valve in Air Conditioner — Working, Function, and Troubleshooting
A 4-way reversing valve is one of the most important components in any heat pump or inverter-type air conditioner. It allows the system to reverse the direction of refrigerant flow, enabling the same unit to provide both cooling in summer and heating in winter. Understanding how it works and how to diagnose common faults helps HVAC technicians maintain system efficiency and performance.
🔹 What is a 4-Way Reversing Valve?
The 4-way reversing valve is a directional control valve installed between the compressor and the indoor/outdoor coils. It has four ports:
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Compressor Discharge (Hot Gas Line)
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Compressor Suction (Return Line)
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Indoor Coil Connection
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Outdoor Coil Connection
Inside the valve is a sliding piston or spool that changes position depending on whether the unit is in heating or cooling mode. This movement is controlled by a solenoid coil that energizes and shifts the slide using refrigerant pressure.
🔹 How It Works in Cooling Mode
When the system is set to cooling, the solenoid coil is usually de-energized. In this position, hot gas from the compressor flows to the outdoor coil, where it releases heat and condenses into liquid.
The indoor coil acts as the evaporator, absorbing heat from the room and cooling the air before it circulates back indoors.
The reversing valve channels refrigerant flow accordingly, ensuring that heat is expelled outside.
🔹 How It Works in Heating Mode
When you switch to heating, the solenoid coil energizes and moves the internal piston. The refrigerant flow reverses direction — the indoor coil now becomes the condenser (releasing heat), and the outdoor coil becomes the evaporator (absorbing heat from the outside air).
This allows the same AC system to deliver warm air indoors even in cold weather, without using separate heating elements.
4 way valve cool mode diagram
4 way valve heat mode diagram
🔹 Common Problems with 4-Way Reversing Valves
Like any mechanical component, the reversing valve can fail due to electrical or mechanical issues. Common problems include:
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Valve Stuck or Sluggish Movement
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Caused by dirt, internal wear, or moisture in the system.
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The AC may blow warm air in cooling mode or fail to switch modes properly.
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Solenoid Coil Failure
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The coil can burn out or lose magnetism.
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You can test it with a multimeter; a healthy coil typically reads 500–800 ohms.
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Internal Leakage
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The piston doesn’t seal correctly, allowing hot gas to mix with low-pressure vapor.
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Symptoms include reduced cooling or heating efficiency and high discharge pressure.
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Improper Installation or Soldering Damage
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Excessive heat during brazing can warp internal seals. Always protect the valve body with a wet cloth during installation.
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🔹 Troubleshooting Tips
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Check voltage at the solenoid coil; ensure power is supplied during heating mode.
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Listen for a “click” sound when switching between modes — no sound may indicate coil or piston failure.
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Use temperature measurements on the four valve ports; improper temperature differences reveal stuck valves or internal leaks.
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Always recover refrigerant before replacing the valve, and vacuum the system properly to remove moisture.
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🔹 Conclusion
The 4-way reversing valve is the heart of any heat pump-type air conditioner, allowing efficient switching between heating and cooling cycles. Proper maintenance, correct installation, and timely troubleshooting can extend its lifespan and ensure consistent comfort in all seasons. Technicians who understand its operation can quickly diagnose issues and keep systems running smoothly year-round.
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