Checking a Heat Pump in Heat Mode – Short #178

In this short podcast, Bryan talks about checking the charge of a heat pump in heat mode. This skill will become more critical as ambient temperatures get cooler.

The most reliable way to check and set the charge regardless of operating mode and season is to weigh the charge. This method is most practical during installation and commissioning, and proper commissioning can prevent issues with charge levels later. Weighing the charge is recommended for big repairs, like major component replacements.

But in many cases, we don't need to check the charge by hooking up gauges; we can check for proper operation by taking a few line temperature readings. Before carrying out any tests or taking readings, make sure the heat pump is defrosted and that you've carried out a full visual inspection. You can carry out a full delivered capacity test in either cooling or heating mode (without the electric heat strips energized) to determine how many BTUs the system is moving. Some simpler tests will require you to compare the discharge vapor line and suction line temperatures to the outdoor temperature and the liquid line temperature to the indoor temperature.

Manufacturers will give specific instructions for their units, including covering the condenser, and they may have charts to help you calculate system pressures based on indoor and outdoor temperatures. If you want to check suction pressure on the low side, you'll always use the common suction port, but you can take either discharge pressure or liquid pressure on the high side.

Bryan also covers:

  • Critical charge
  • Ductless system charging practices
  • Some manufacturer-specific practices
  • Indoor temperatures and system pressures
  • R-22 rules of thumb
  • Total discharge superheat
  • Staging and capacity considerations
  • Weighing out when in doubt

Read the tech tip about this topic at

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