The answer to 'evaporator coil not turning on' is that there are several common causes, including a faulty thermostat, a tripped circuit breaker, a problem with the blower motor, or issues with the refrigerant lines. Symptoms may include warm air coming from the vents, high humidity, or the system not turning on at all.
If the evaporator coil is not turning on, first check the thermostat to ensure it is set to 'cool' and the temperature is set lower than the current room temperature. Next, check the circuit breaker or fuse that powers the HVAC system to make sure it has not tripped or blown. If the thermostat and power are working, the issue may be with the blower motor or the refrigerant lines. These types of problems often require professional diagnosis and repair, so it's best to call an HVAC technician if you can't identify and fix the issue yourself.