The answer to 'evaporator coil not heating' is that the most common causes are a refrigerant leak, a problem with the thermostat or control system, or a malfunctioning blower fan. Symptoms include the air coming from the vents not feeling as cold as it should, the coil itself not getting cold, and the system not properly cooling the home.
Potential solutions include checking the refrigerant level, inspecting the thermostat and control wiring, and ensuring the blower fan is running properly. However, many of these issues require professional diagnosis and repair, so it's generally best to call an HVAC technician if the evaporator coil is not heating as it should.