Several factors that can cause system freezing. First, if running in the cooling mode check your filters; restrictions in air flow can lead to freezing. Next, thaw the system out by turning off the cooling and running the fan. Also, try turning the system to the heat mode until the ice has melted. If the problem recurs after checking for air restrictions and thawing your system .Give us a call and our service technicians will check the refrigerant level. They may also have to clean the evaporator coil, check the blower speed and check for any intermittent in blower operation. A service technician can also evaluate other conditions that may make your system prone to freezing and recommend the best course of action.