The answer to 'evaporator coil not heating' is that the most common causes are a refrigerant leak, a problem with the blower fan, or an issue with the thermostat or control system. Symptoms can include the air coming from the vents feeling cool but not cold, the system running continuously, or the evaporator coil freezing up. Solutions may involve repairing refrigerant leaks, replacing the blower fan, or resetting or replacing the thermostat.
In many cases, the evaporator coil issue is a sign of a larger problem in the HVAC system. While some basic troubleshooting can be done at home, it's generally recommended to call in a professional HVAC technician to properly diagnose and fix the problem. Attempting DIY repairs on the evaporator coil or other HVAC components can be dangerous and may end up causing more damage if not done correctly.