Heat Pump Reversing Valve 101


The reversing valve; the second most confusing part of a heat pump
(Yes, the defrost board still holds first place for the most confusing part)

So, what’s the confusion about heat pump reversing valves?

The confusion is understandable; a big round cylinder with three large tube connections on top, a smaller connection on the bottom (wait, there’s both a top and bottom?) and a miniature solenoid valve with three tiny tubes hanging off the side…scary.

The reversing valve is the heart of a heat pump, without it, there is no heat pump.

 The good news is they’re easy to troubleshoot, once you understand its purpose and how it operates.

What’s it do?

The reversing valve swaps the compressor’s suction line with its discharge line, making the indoor coil the condenser and the outdoor coil the evaporator.

What are the four pipe connections for?

Heat Pump Reversing Valve The valve has four ports; three ports on the top, and one port on the bottom.  The bottom port is always connected to the compressors discharge port, always.  The top center port is always connected to the compressors suction port; always.

Etch this in your brain: the small bottom port is ALWAYS piped to the compressor discharge and the top middle port is ALWAYS connected to the compressor suction port.

What about the other two connections on a reversing valve?

The remaining two ports are outlets. One connects to the suction tube going to the indoor coil, the other connects to the hot gas discharge tube going to the outdoor coil.

How does a heat pump reversing valve work?

Inside the reversing valve is a sliding piston with ports. Sliding the piston to one side or the other connects the hot gas and suction ports from the compressor to either the indoor or outdoor coils depending on what mode the system is operating in.

What makes the piston slide?

A small capillary tube runs from the valves hot gas port (bottom port) to a small solenoid valve where it is directed to one side or the other of the main valve body. The high pressure pushes the piston from one side to the other. The direction the piston moves depends on whether the solenoid is energized or not.

Next: troubleshooting reversing valves


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Patrick is Zen HVAC’s diagnostic and training guy. Patrick started in the trade the day he left technical school and never looked back. He's served in various technical and training roles in the HVAC industry but specializes in system troubleshooting and diagnostics, retro commissioning, and technical training. His moto: If I can understand it, anybody can. Patrick uses the Zen common sense approach to teach Patrick’s Likes- His Wife, kids and dog. Old pickup trucks. Hiking. The industrial Revolution. Patrick’s Dislikes- Taking work too seriously. Anything unintuitive. Emoticons :( Patrick’s Favorite famous person- Theodore Roosevelt “I am only an average man, But I work harder at it than the average man" Famous Patrick Quote- “Well, that was stupid of me”

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2 comments on “Heat Pump Reversing Valve 101
  1. Heat pumps work exactly the same as air conditioners with the exception that they are equipped with a reversing valve. The reversing valve allows the refrigerant cycle to reverse and move heat from outdoors to inside your home during the cold months.

  2. Yuri says:

    Nice content! Please keep posting more. It really helps 🙂

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