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HVAC School - For Techs, By Techs

Jan 16, 2020

In this face-to-face discussion, Bryan and Kaleb share some tips for diagnosing and replacing the reversing valve on a heat pump. These valves may also be known as four-way valves.

Kaleb and a trainee recently had to diagnose a heat pump with a scroll compressor. The motor was also over-amping due to a failed capacitor, and the compressor was making a metallic grinding noise. Because reversing valves are pilot-activated, they need a pressure differential to shift, so the scroll plate can sometimes pop up and make noise during bypass. Another possibility was that the compressor could have been running backward, but that wasn't the case.

There are some cases when techs misdiagnose a compressor problem as a reversing valve failure; however, in Kaleb's case, there was a problem with the reversing valve that then caused compressor failure.

To determine if a system has a reversing valve issue, you should look at the temperature difference across the valve (more than 3 degrees). Another thing to look for is an abnormally low compression ratio (high suction, low head pressure). You also want to watch the compressor amperage, as it will likely be lower than normal. When doing more advanced tests, such as delivered capacity tests, use Bluetooth tools to make your life a lot easier; that way, you can clamp your probes on.

When Kaleb replaces a reversing valve, he cuts them out wherever possible. If he can't cut them out, he sweats them out and sweats the new one in. Sometimes, it's also easier to remove the entire condenser coil during replacement.

Kaleb and Bryan also discuss:

  • Common suction port
  • Causes of compressor damage
  • Unreasonably hot discharge lines
  • Compressor amperage drop
  • Common suction, common discharge lines
  • Kaleb's compressor replacement
  • Cutting out suction dryers
  • Sweating out reversing valves in Trane units
  • Purging with nitrogen before a pressure test
  • Deburring properly

Learn more about Refrigeration Technologies HERE.

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