There is an inflexible belief here that freezing evaporator coils in the heat pumps is caused by low refrigerant. Always low refrigerant. We spend a lot on low refrigerant service calls.

Consider the following statement.

Low refrigerant levels: If your air conditioner has a refrigerant leak it will not have an adequate amount of refrigerant to absorb heat from your home’s air. Without something to remove the heat, the coils can freeze up.
My background is mostly theoretical so I am open to the possibility that low refrigerant could cause evaporator freezing. But I need something more rational than the above statement to convince me. Is there something I am missing?

The units are cheap 3-4 ton split systems with piston expansion devices. Most are R22, though the present problem child has R410.

Thanks;
Doug