The answer to 'my evaporator coil won't turn on' is that there could be several common causes, including a faulty thermostat, a problem with the electrical wiring or controls, or a malfunctioning evaporator fan motor. The symptoms may include no airflow from the vents, the system not cooling properly, or the evaporator coil icing up.
Some potential solutions include checking the thermostat settings, inspecting the electrical connections, and cleaning or replacing the evaporator fan motor. However, it's generally best to call a professional HVAC technician to diagnose and repair the issue, as they have the specialized tools and expertise to properly identify and fix the problem.