Reversing Valve
The four way valve that lets a heat pump swap the roles of the indoor and outdoor coils.
Safety
What it is
A reversing valve is a four way valve that redirects compressor discharge gas either to the outdoor coil for cooling or to the indoor coil for heating. A small pilot solenoid uses pressure difference to move the main slide inside the valve body.
Compressor: The compressor raises refrigerant pressure and temperature, so hot discharge gas leaves it in either mode.
How it works
Energizing the solenoid shifts a pilot valve, which vents pressure from one end of the slide. The pressure difference across the slide pushes it to the other end, changing which coil receives discharge gas. Because the valve relies on pressure difference, it will not shift reliably if the system pressures are too close, such as with a very low charge or a weak compressor.
Manufacturers differ on whether the solenoid is energized in heating or in cooling. Check the wiring diagram for the specific unit before concluding the valve is stuck.
How to diagnose it
Measure 24 volts at the solenoid coil in the mode that should energize it
No voltage means the fault is in the board or thermostat wiring, not the valve
Feel or measure the temperature of the three lines leaving the valve body
A valve that is not fully shifted often leaves the lines closer in temperature than they should be
Compare suction and discharge pressures against the mode
A leaking valve shows an unusually high suction pressure and a low discharge pressure together
Listen for the valve shifting when switching modes
A distinct whoosh indicates the slide moved
Verify charge and compressor performance before condemning the valve
A weak compressor cannot create the pressure difference the valve needs
Tap the valve body lightly while switching modes as a diagnostic only
A valve that shifts only when tapped is sticking internally and should be replaced
Replacement requires refrigerant handling
Tools involved
- Digital manifold with temperature clamps
- Multimeter
- Recovery machine and cylinder
- Nitrogen regulator and brazing equipment
Symptoms
Practice & Mastery
- Questions1
- Reversing Valve Troubleshooting Scenarios2
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