A frozen evaporator coil is the reason a central air conditioning system freezes up. The coil is the component of the system responsible for transferring heat from the home’s interior to its exterior.
Evaporator coils freeze up for one of two reasons. The airflow across the coil may be obstructed or the system lacks enough refrigerant. In either case, the evaporator coil fails to dissipate heat properly and the system itself becomes too cold.
When the system is super-cooled, condensation forms on the coils and eventually turns to ice. In effect, this turns the air conditioning unit into an old-fashioned icebox.
Here is what you should do if your system is frozen:
1. Use the thermostat to turn the system off and do not stop at just moving the temperature setting. Turn the entire air conditioning system off by flipping the switch to the off position.
2. Inspect the system for any areas where airflow is obstructed. Remove the old air handler or furnace filters and replace them with new ones. Open the registers and make sure drapery or furniture is not blocking the airflow near them.
3. If the system is still freezing up, call a local repair service for professional help.