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Problem: My heat pump is making a funny noise. How does a reversing valve work?

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Problem: My heat pump is making a funny hissing noise. It sounds like the reversing valve is not working. How does a reversing valve work?

Answer: Yes, if your heat pump reversing valve is not shifting or is stuck in between the heating and cooling mode then you heat pump will make a funny hissing sound or not sound normal. A heat pump which is low on refrigerant charge or has a stuck reversing valve can cause this problem.  Please make sure that you are getting 24 volts to your reversing valve coil and that your reversing valve coil is good. If your reversing valve is stuck I would suggest that you check or have your heat pump system refrigerant charge checked. Sometimes when I was doing service I would try to connect and disconnect the orange wire (this is the wire that most of the time controls the reversing valve) and see if the valve shifts. Sometimes a light tap with a rubber mallet on the valve can get the valve to unstick. Make sure you do not dent the valve because a dent will make the reversing valve stick even more. FYI: Many people and service techs, including myself have a hard time diagnosing the difference between a stuck reversing valve and a blown valve on a compressor. The sound the unit makes with a blown valve on the compressor and a stuck reversing valve are real similar. Below we have a YouTube video made by Supercool Slide Rule which shows how to test a reversing valve coil. Below we also have another real good informative YouTube video made by grayfurnaceman which explains how a reversing valve operates. Thanks to Supercool Slide Rule and grayfurnaceman for making these informativ video! If a reversing valve is stuck most of the time it requires replacing the reversing valve. If you have any other questions please feel free to email us: support@arnoldservice.com or comment below. Hope you have a nice day! We would love to help you out and have your business!

4 thoughts on “Problem: My heat pump is making a funny noise. How does a reversing valve work?

  1. My Trane heat pump is icing at outside unit . Then noticed low pressure (large tube) was extremely hot at evaporator coil. Hissing sound heard at evp. coil. Could this be a reversing valve failure, stuck or leaking? Note: unit is 16 years old. Charge was added to unit first of summer, tech did not find any leaks. Could over charge cause above issues? High side #275 running load amps within range lower than nameplate.

    1. Hi Paul! Yes, this sounds like the reversing valve is not shifting. I believe that on Trane units the reversing valve coil is energized in the cooling mode constantly. So if you have your thermostat set on “Cool” the reversing valve coil should be energized. I would like to suggest setting your thermostat to cool and testing the voltage going to the reversing valve coil to see if it is getting 24 to 28 volts AC. If it is not getting the 24 volts then you might have a thermostat problem, a thermostat wire problem or a defrost control board problem. The thermostat should send the 24 volts to the reversing valve coil through the “O” wire on your thermostat. If the reversing valve coil is getting 24 volts and not shifting then you might need a new reversing valve. I hope you can find an easy inexpensive solution to the problem. Steve

  2. Our heat pump keeps making a strange noise and our dog will not stop barking at it. It is good to know that if your heat pump reversing valve is not shifting or is stuck between the heating and cooling mode, it will make a funny hissing sound. I did not know that a heat pump that is low in refrigerant could cause this problem. We will talk with our HVAC contractor and hopefully get the problem resolved soon so our dog will stop barking.

    1. Yes, I would suggest that you get your heat pump looked at by a professional. I hope it is an easy and inexpensive fix. Steve

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