The answer to 'zone control system blowing cold air' is that there could be several common causes, including a problem with the thermostat, damper motors, or the zone control panel itself. Symptoms may include some rooms being too cold while others are comfortable, or the system cycling on and off frequently.
Some potential solutions include checking the thermostat settings, inspecting the damper motors to ensure they are opening and closing properly, and troubleshooting the zone control panel for any error codes or malfunctions. If you're not comfortable diagnosing and repairing the issue yourself, it's best to call in a professional HVAC technician who can properly identify and fix the problem.