Home › Air Conditioners › Parts › Reversing (4-way) valve

Air Conditioner Reversing (4-way) valve: What It Does and Signs It's Failing

Found only on heat pump models, this brass valve near the compressor in the outdoor unit switches the direction of refrigerant flow. That's what lets the same system cool in summer, heat in winter and defrost the outdoor coil.

Who should replace it

Technician job

Related codes

3 error codes on this site point to this part.

How it works

An electric coil on the valve moves a pilot slide that shifts the main valve. Flip the flow and the indoor coil becomes the hot side instead of the cold one.

Signs it is failing

Unit blows cold air in heat mode or warm air in cool mode
Stuck in one mode
No whoosh of refrigerant when the unit switches modes or starts a defrost
4-way valve or mode-switching codes

Mode and 4-way valve codes point here, but Daikin and Fujitsu also list the coil, thermistors, the outdoor board and low refrigerant as possible causes.

Can you replace it yourself?

Make sure all indoor units are set to the same mode; mode conflict codes are just a setting. Coil and valve diagnosis involves live voltage, and the valve body is brazed into the sealed system. Swapping the valve body means recovering and recharging refrigerant, a job reserved in the US for EPA Section 608-certified technicians.

Always unplug the air conditioner or switch off its breaker before opening any panel, and turn off water or gas where relevant.

Buying the right part

Leave ordering to the tech; the coil voltage and valve size are model-specific.

Error codes linked to the reversing (4-way) valve

Last reviewed 2026-10-19.

Sources we checked