Heat Pump Reversing Valve.

The heat pump reversing valve is the only difference between the heat pump and standard air conditioner. Previously we have talked about how a heat pump works. We concluded it works just like an air conditioner, moving heat from one place to another.  But the heat pump reversing valve  allows us to move the heat from inside the house to the outdoors (cooling mode) or to reverse the cycle and remove the heat from outside the house to the indoors (heating mode).

But how does it really work? And what does it look like? That’s what we are about to discover in this section.

Frist let’s see what a heat pump reversing valve looks like. In the figure below, you will notice the valve has 4 tubes or connections; A, B, C, D. This valve is also referred to as a 4-way valve.

Heat Pump Reversing Valve

A heat pump reversing valve is an electro-mechanical 4-way valve that reverses the refrigerant (Freon) flow direction, using an electrical magnet.  It works very similar to your washer’s water valve or solenoid valve (pictured below). When you connect electricity to a valve (energize it), it opens and lets water in and when you disconnect the electricity (de-energize it), it closes the valve and the water stops flowing.

Washer water solenoid valve

When you energize the coil with electricity (in the USA, washer’s water valve use 110VAC, and in most other countries, they use 220VAC) the coil becomes magnetized, pulling a pin and compressing the spring. This action opens the valve to let the water flow. When you de-energize the coil the electrical magnet loses its magnetic power, and the compressed spring expands and pushes the pin back to shut off the water.

The washer’s water valve (solenoid valve) is 2-way valve, and in the Heat Pump, the reversing valve is 4-way valve. Let’s look at the image below so we can understand it better.

  • Energized mode, cooling mode
Heat pump reversing valve energized in cooling mode

The heat pump reversing valve has 4 large tubes (A, B, C, D ) that’s why they call it a 4 way valve and it also has:- capillary tube (1), capillary tube (2), capillary tube (3), slider (4), block (5) ,electrical coil (6), electrical magnet (7), and spring (8).

Notice that the compressor’s discharge port (high pressure) is always connected to tube A in the reversing valve and the return port (low pressure) in the compressor is always connected to tube B. Therefore tube A always has higher pressure refrigerant, and tube B always has lower pressure refrigerant. Notice also that capillary (2) is always connected to tube A, thus capillary (2) also has a high pressure.

When we energize the electrical coil (6) it energizes the magnet (7) that pulls the block (5) which will blocks the capillary tube (3) and compresses the spring (8). Wow if that was confusing, well if it was, please read it one more time.

Got it? Great, so notice that the capillary tube (3) is now blocked, and the high pressure refrigerant will flow from capillary (2) to capillary (1 ) straight to the left side of theheat pump  reversing valve’s body that will push the slider to right hand side from the valve’s body which will allow the high pressure refrigerant to go from the tube A to tube D to the outdoor coil, through the metering device to drop its pressure, then to the indoor coil to cool the inside of the house ( cooling mode ) then back to tube C .

If you had notice the slider has a top grove which allows the low pressure refrigerant to flow from tube C to tube B then back to the return port in the compressor to repeat the cycle again.

That was easy wasn't it? Now let’s see what happens in heating mode in the figure below.

  • De-energized mode, heating mode
Heat pump reversing valve de energized in heating mode

Please notice that the coil (6) lost its power, or de-energized, which makes the electrical magnet (7) lose its magnetic power.  When this occurs, the spring (8) will decompress and push the block (5) to the left, and block the capillary tube (1). I am thinking you are becoming an expert by now!

The capillary tube (1) is now blocked and the high pressure refrigerant will flow from capillary (2) to capillary (3) straight to the right side from the reversing valve’s body. This in turn will push the slider to the left hand side of the valve’s body,which will allow the high pressure refrigerant to go from the tube A to tube C. This allows refrigerant to flow to the indoor coil to heat the inside of the house (heating mode),  then through the metering device to drop its pressure then to the outdoor coil then back to tube D.

Again the slider has a top grove this will allow the low pressure refrigerant to flow from tube D to tube B then back to the return port in the compressor to repeat the cycle again. That’s it that’s how the heat pump reversing valve works in real-life.

We should notice some important stuff:

  • When we energize the reversing valve we start the cooling mode, and when we de-energize it, we start the heating mode. Is this always the case or can it be the other way around? Yes of course it can. However, in almost all Heat Pumps, the cooling mode starts when we energize the reversing valve, so if the electrical coil fails (and it cannot energize the reversing valve anymore) you will be able to have a heating function and you won’t freeze your butt off.      
  • All reversing valves use 24VAC to energize, unlike a washer’s water valve which uses either 110VAC or 220VAC.       
  • Reversing valves use the difference between high and low pressure refrigerant to work, the compressor should be working in order for the reversing valve to work properly.       
  • 99% of the reversing valve failures are due to bad or faulty electrical coil and not because the valve itself has failed. So the next time an air conditioning service man tells you that you need to change the reversing valve, chances are he doesn't know what he is talking about or he want to rip you off. .      
  • Replacing the reversing valve could be a complicated process. It needs a very skilled person, because the reversing valve will be soldered, which can easily overheat the reversing valve’s body, and in turn melt the slider inside it, making it inoperable.      
  • if you really need to replace your valve, and your unit is over 10 years of age, please consider replacing the Heat Pump.      
  • The heat pump reversing valve itself might cost $200-$250 however, it will take a lot of work ,1st the technician must recover all the refrigerant (Freon) in the approved and certified container , if he lets it out to the air or like a lot of them do into a bucket of water that’s violation to the law (it could cost him $10,000 if you report him) , after he needs to take out the electrical coil then takes out the old reversing valve and buts the new one in and soldered it carefully, then vacuum the system and make sure there is no leaks , then charges it back with refrigerant (Freon). All that will take time and effort but it should not exceed than $900 and as always if you end up doing any repair work only deal with people charge by labor and material and not lump sum.

Well that’s it folks I hope you have a better understanding of the heat pump reversing valve. As always the more you know the less likely you are to get ripped off!



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