Is there an easy way to tell if a mini-split ductless unit is low on refrigerant? Yes, if the Delta T is low and the system continues to run without reaching the desired temperature, you can check the total superheat to determine if it is low on refrigerant. I have noticed that on most properly charged systems, the total superheat tends to be between 0 to 5 degrees during emergency cool and full speed cooling. The reason that the system can run with this low of a total superheat is that the accumulator tank protects the compressor from saturated refrigerant entering in. Mini-splits make a better use of the space in the evaporator coil and run at a lower superheat than conventional single or two speed compressor systems. If the system is low on refrigerant, the total superheat will be high. If you see a system running at full cooling capacity (including all of the indoor head units running in a/c mode) and the superheat is 12 degrees or higher, there is likely a problem with the charge. To learn more about the full process of checking the refrigerant charge of a mini-split ductless system, check out this full length article on Mini-Split Ductless Charging!
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