The answer to 'why is my evaporator coil not turning on' is that there could be several common causes, such as a faulty thermostat, a tripped circuit breaker, or issues with the air conditioner's electrical components. Symptoms may include warm air coming from the vents, the fan not running, or the compressor not kicking on.
Before calling a professional HVAC technician, you can try some basic troubleshooting steps. First, check the thermostat to make sure it's set to 'cool' and the temperature is set below the current room temperature. Next, locate the circuit breaker for the air conditioning unit and make sure it hasn't tripped. If the breaker is fine, you may need to replace the thermostat or have an electrician inspect the wiring. However, if you're not comfortable working with electrical components, it's best to call a licensed HVAC technician to diagnose and repair the issue.