Reversing valve
The valve that redirects refrigerant flow so a heat pump can switch between heating and cooling. A valve that sticks part-way through a changeover produces the classic symptom of a system that cools when heat is called for, or the reverse.
Also called four-way valve, changeover valve
What does a reversing valve do?
The reversing valve is the four-way valve that swaps which coil condenses and which evaporates. It is the single component that lets one heat pump both heat and cool.
Reversing valve: how it works
A solenoid shifts an internal slide that re-routes compressor discharge to one coil or the other. Whichever coil receives hot discharge gas becomes the condenser, so the same hardware heats or cools depending only on which way the valve is set. Defrost uses the same movement briefly to send hot gas to the outdoor coil.
Where you meet the term
- In a complaint of cool air on a heat call, where the valve did not complete its changeover.
- In a defrost sequence, where the valve shifts, the outdoor fan stops, and the indoor fan is held off.
- In a service diagnosis, where valve body temperatures across the four ports are compared to see whether the slide moved.
How to check it
- Confirm the mode the controller is actually set to. Auto modes and heat pump systems paired with unfamiliar thermostats can be calling for the mode you are not expecting. Check the display before the hardware. Owner check
- Wait out a defrost cycle before judging. Cool air during defrost is the valve working correctly. A cycle lasts minutes, not hours, and ends with heating resuming. Owner check
- Compare port temperatures across the valve body. Discharge, suction, and the two coil ports should show a clear pattern for the commanded mode. A blurred pattern indicates a slide that has not seated. Technician
Reversing valve: what it is not
- Cool air in heating is not always the valve. Defrost, a low outdoor temperature, and a control set to the wrong mode produce the same complaint.
- The solenoid coil and the valve body are separate failures. An electrically dead coil and a mechanically stuck slide need different repairs.
Reversing valve questions
Why does my heat pump blow cold in heating?
The most direct explanations are a defrost cycle in progress, a control set to cooling, or a reversing valve that has not completed its changeover. The first two are checked from the room before anyone opens the unit.
Does the reversing valve make a noise when it changes?
Yes. A distinct hiss or thump as the slide shifts and pressures equalise is normal, and hearing it confirms the valve moved when the mode changed.
Can a reversing valve be replaced?
Yes, but it is a brazed component in a sealed refrigerant circuit, so it requires recovery, replacement, evacuation, and recharge by a certified technician.
Where this definition comes from
Written from manufacturer support article, operation manual material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- Why Is My Mini-Split Not Working in Heat Mode?Trane ductless heating checks covering controls, airflow, outdoor clearance, and service conditions.
- ADUH LUAS1 Operating ManualADUH07, ADUH09, ADUH12, ADUH18, and ADUH24 LUAS1 operation, defrost, filter care, and normal behavior.