How a Reversing Valve on Heat Pump Works in 2022!

reversing valve on heat pump

How a Reversing Valve on a Heat Pump Works!

Heat pump systems act like air conditioning systems with a reversing valve to redirect the refrigerant flow to the outside condensing coil from the discharge line in summer.

The reversing valve can redirect that refrigerant flow towards the indoor evaporator coil, making it the condenser coil for heating purposes in winter.

If you need help understanding how a heat pump works, it’s best to read this article first: How Does a Heat Pump Work?

In addition to the heat pump reversing valve, most heat pumps have two separate metering devices. One inside and one outside.

The outdoor metering device is used for the heating cycle in winter when the outdoor coil is now the evaporator coil.

The indoor metering device monitors the cooling mode during summer when the indoor coil plays its usual role as the cold side of the air conditioner.

How Reversing Valves Work!

Breakdown of a heat pump reversing valve

🧊 Reversing Valve

The reversing valve is made up of two primary parts.

The valve, which looks like a small cylindrical metal component directs the flow of refrigerant within the heat pump.

Secondly, you have the suction line and discharge line, which allow for the movement of the refrigerant to and from the reversing valve.

The reversing valve is sometimes called a changeover or a 4-way valve.

The refrigerant from the compressor discharge (high pressure) is directed into the top of the valve. 

The valve itself has four ports which are tube-like fingers protruding out of the cylindrical body.

First, the top port receives the refrigerant from the discharge line.

Then, depending on whether the reversing valve is energized or de-energized, the other 3 ports on the bottom direct the refrigerant.

Which ports are active depends on whether the heat pump is in heating or cooling mode.

The center port on the bottom is always the suction line.

The sliding mechanism in reversing valve slides, allowing the refrigerant to flow to the correct coil.

This allows the suction gas to be rediverted.

The reserving valve works with the help of another component called an electromagnetic solenoid which operates the slider.

🧊 Electromagnetic Solenoid

Generally, when the solenoid is energized, the heat pump works in cooling mode sending the discharge gas to the outdoor coil.

Many manufacturers use this as the standard setup.

However, some manufacturers (such as Rheem or Ruud) may operate in reverse, so it’s best to call in an HVAC professional before working on a heat pump.

When the electromagnetic solenoid energizes, it slides over a pilot valve which acts as a small reversing valve inside the reversing valve.

This redirects the flows creating a pressure differential on one side of the valve, which forces the slide over to operate in cooling mode.

An extra note is that it isn’t the electromagnet that drives the heat pump reversing valve but the pilot valve that uses the pressure created by the compressor to slide the valve.

This is important as if your compressor isn’t pumping correctly, the reversing valve will not shift.

This is because the valve does not cause the valve to shift; it’s the pressure of the refrigerant in the discharge line from the compressor.

So the pressure difference between the discharge and suction lines is what slides the valve into the correct mode.

When the heat pump unit is switched off, the heat pump reversing valve will not shift between modes when the pressures are equalized.

How the Indoor and Outdoor Coils Operate

layout of the evaporator and condensing coils in a central HVAC system

The indoor coil becomes the condenser coil in heating mode, which acts as a heat rejector.

The outdoor coil becomes the evaporator coil, which is now the heat absorber.

You pick up heat from the outside and reject it inside in this mode.

This creates a heating effect for the occupants in the home.

The compressor in a heat pump continues to operate the same as a standard air conditioner, which is to move the refrigerant through the system.

However, the reversing valve interrupts those flows and redirects them in either direction based on the heating and cooling mode.

How a Reversing Valve on Heat Pump Works

A reversing valve uses a 24-volt electromagnetic solenoid to activate a smaller pilot valve which uses compressor force to drive the reversing valve back and forth, changing the flow of refrigerant, allowing you to operate your heat pump as an AC in summer and a heater in the winter months.

For homeowners looking to change modes, it’s as easy as just hitting a button on your dual-mode thermostat to reverse the flow of refrigerant.

If you have a heat pump that’s not working correctly or want to learn more about heat pumps, then don’t hesitate to find out if Phyxter Home Services is in your area. 

Related Reading: Heat Pump vs Furnace – The Pros and Cons of Each Heating Type

Jake Gibson

CEO @ Phyxter and HVAC Guru

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Phyxter (pronounced Fix-ter) is a national home services brand specializing in Residential HVAC, Electrical and Plumbing solutions.

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