The answer to 'heat exchanger freezing up' is that a frozen heat exchanger is a common issue with HVAC systems, often caused by a lack of airflow or a refrigerant leak. Symptoms include the unit blowing cold air, ice buildup on the coils, and reduced heating capacity. Solutions can include cleaning the air filters, checking the refrigerant level, or addressing any airflow obstructions. However, if the issue persists or you're unsure of the cause, it's best to call a professional HVAC technician to diagnose and repair the problem.
A frozen heat exchanger can be a serious issue that requires prompt attention to prevent further damage to the system. Trying to DIY the repair may end up causing more harm than good, so it's generally recommended to have a licensed HVAC technician inspect and service the unit.