If your system is freezing during the cooling cycle it is most likely the loss of air flow. Most systems use 1 inch thick pleated filters that need to be changed every month in our south east climate. In addition to the filters semiannual maintenance can keep the system from freezing due to air flow by cleaning the coils every 6 months and the blower wheel as needed. Refrigerant leaks may also play a role in freezing systems. If your system is freezing outside during the heat cycles you likely have a heat pump. A properly running system will initiate a defrost cycle if the system is frozen. Usually this is done at 30, 60, or 90 minute intervals and can last for up to 10 minutes. If the system is unable to thaw the ice during the defrost cycle it is likely having a problem or you are experiencing freezing rain. Spraying water from a hose on to the ice can help thaw the ice and allow the system to heat while you wait for your service technician to arrive.