The answer to 'furnace freezing up' is that a frozen furnace is a common problem that can have several underlying causes. The most common reasons are a clogged air filter, low refrigerant levels, or a problem with the defrost cycle. Symptoms include ice buildup on the coils, reduced airflow, and the furnace cycling on and off frequently.
In many cases, the issue can be resolved with some basic troubleshooting and maintenance. Homeowners can try changing the air filter, clearing any blockages around the unit, and checking the refrigerant levels. However, if the problem persists or you're not comfortable working on the furnace, it's best to call in a professional HVAC technician to diagnose and repair the issue.