The answer to 'zone control system freezing up' is that a common cause is a problem with the thermostat or zone dampers. Symptoms can include the system blowing cold air, ice buildup on the coils, or uneven temperatures in the home. Solutions may involve adjusting the thermostat settings, cleaning or replacing the zone dampers, or checking for airflow obstructions.
If the issue persists or you're not comfortable troubleshooting the system, it's best to call a professional HVAC technician. They can diagnose the root cause and make the necessary repairs to get your zone control system working properly again.