HVAC for both cooling and heat uses a different fan speeds. Cooling the fan speed is usually higher, for heat the fan speed is lower. Depending on your model, same fans are multi speed, others are variable speed. It all depends on the design of the controller and the SEER rating. The condenser fans can also be variable or multi speed, again depending on the model. Variable speed fans will usually get a 1 SEER improvement for its rating.
Coils will only freeze if the airflow is restricted (such as by a dirty filter) or the refrigerant is low (pressure) and the temperature of the coils will get below 32*F. For cooling the fan runs higher than in heat mode. Too fast and the air won't have time to cool and humidity extracted from the air. Too slow and the airflow to the furthest rooms may not be sufficient. From the old R22 units to today's HE units, air volume has been increased by larger duct work and not by fan speed. If your ductwork is undersized, increasing the fan speed will help but the efficiency may drop just a bit. Anyway, you'll see a big drop on your electric bill and the home should be more comfortable. Two stage cooling is usually a high end unit and most likely variable speed fans are used.