The answer to 'why is my furnace freezing up' is that a frozen furnace is typically caused by a problem with the airflow or refrigerant levels in the system. This can happen when the air filter is clogged, the blower is malfunctioning, or there is a refrigerant leak. A frozen furnace can lead to other issues like reduced heating output or even a complete system failure.
Some common symptoms of a frozen furnace include ice buildup on the coils or vents, reduced airflow, and the furnace cycling on and off frequently. To fix a frozen furnace, you'll need to identify and address the underlying cause, which may involve cleaning or replacing the air filter, repairing the blower, or recharging the refrigerant.