The answer to 'my evaporator coil won't turn on' is that there could be several common causes, such as a failed thermostat, a problem with the electrical supply, or a malfunctioning blower motor. Symptoms may include no airflow from the vents, the system not turning on at all, or the coil icing up.
Some potential solutions you can try yourself include checking the thermostat settings, inspecting the air filters, and resetting any circuit breakers. However, if the issue persists or you're not comfortable troubleshooting the electrical components, it's best to call in a professional HVAC technician to diagnose and repair the problem.