Final answer:
The most likely reason for the outdoor coil freezing solid on a 'no heat' service call is a low refrigerant charge.
Step-by-step explanation:
The most likely reason for the outdoor coil freezing solid on a 'no heat' service call is a low refrigerant charge.
When the refrigerant charge is low, the pressure inside the system drops, causing the coil to get colder. As a result, the moisture in the air condenses on the coil and freezes. This can block the airflow, leading to a lack of heat transfer and causing the system to lose its heating capability.
It is important to consult a professional HVAC technician to diagnose and fix the issue.