Here are 6 Key Balancing Factors for the refrigeration charge of the SunPump, in sequential order.


  1. Equalized pressures are in the 190 - 210 PSI gauge range at 20 C. indoor temperature when the compressor is off for 5 minutes or longer;

  2. The Sight Glass shows a steady stream and yellow indicator after 10 minutes of operating. Be patient with adding R410a slowly and giving time for the system to normalize. An early look may not be a true indicator if it is too soon;

  3. High Pressure gauge reaches over 400 PSI, to as high as 450 PSI on a cool day, and 500 PSI on a warm afternoon with Sun on the panels. Pressures above 550 to 600 PSI is too much refrigerant, and below 350-400 PSI is too little on a 20 C day. The colder the temperature, the lower the pressures;

  4. Sub-Cooling of 8-12 F. temperature difference is a good range.

  5. Using a clamp Ammeter, the Compressor Amps match the label rating when the water set point temperature of 55 C (131 F.) is reached. For example a 14 kW SP3.1 should rise from the mid-teens as the water gets hot and draw 18.4 amps when the 131 F set point turns it off. If the Amps is too high that indicates too much refrigerant or work load on the Compressor.

  6. The Panels show frost on the lower portion of the panel, but is black on the upper, during a cold morning in the 0-10 C range is a good visual indicator they are working. The Panels should not be completely covered in frost above 0 C, but partial is expected. 


My suggestion is to examine most or all of the above factors to establish the right balance of R410a charge. The pre-charge amount is close when the line set is under 15 feet, but could see 10-50 ounces added for long lengths and more panels. Please mark the amount added in the equipment area so we can know the current status.


The Controller only needs the date and time set, the other defaults are acceptable. A sub-zero Winter install may want to go right to Hybrid Mode (Heat Pump priority with Electric element boost), Click the Power button to reveal a column of 6 blue icons, click the M icon twice to move the Mode from HP (Heat Pump) to HY(HYbrid). See the Owner Manual for more details or this link for short YouTube Video demonstrations. 4 YouTube Videos - SP3.1 Controller How To