What is the difference between heat pumps that are listed as limited range or maximum range?

A limited range heat pump is not a defrosting unit in heat mode. Heat pump operation ceases at approximately 35 degrees F (1.6 C) outside temperature and electric resistance heater in the air handler (if supplied) is the sole source of heat. The 52HA, T2HA, T3HA, and T4HA Series of outdoor units are limited range heat pumps. S1HA single zone condensers are maximum range heat pumps, which operate down to 0 degrees F with defrost cycle.

The S1HA condensing unit will energize the electric heater on the indoor evaporator (if supplied) during the Defrost Cycle to dampen the cold air that is discharged off the coil during the Defrost Cycle.