Checking Mini Split Inverter Refrigerant Charge

 May 12, 2025      Rick Virgili

Having the correct refrigerant charge in a mini split inverter is critical because an incorrect charge, whether too high (overcharged) or too low, can significantly impact the system. These can negatively affect efficiency and cooling performance. It can even damage the compressor by causing issues like liquid refrigerant flooding the accumulator and entering its cylinders, leading to reduced lifespan and potential breakdowns. 

The problem technicians run into is that this is not your typical refrigerant system where you can just check the charge with the subcooling or superheat method. Because these inverter systems use EEV’s (electric expansion valves) and multiple sensors, the system is constantly adjusting the compressor and fan speeds. Therefore, the system can run in a very low to no super heat condition.

The only proper way to check the charge of a mini split inverter system is to recover all refrigerant into the proper recovery container. If the unit is low compared to the factory charge, plus the trim charge listed on the unit (the additional amount added), then a leak test should be performed. Finally, repair any leaks found, pull a vacuum, and then recharge by weighing in refrigerant to factory charge plus trim charge specs listed on the outdoor unit.

As always, if you need assistance please call the Famous Supply HVAC Tech Support Department at 330-475-8230.