The answer to 'why is my air handler not turning on' is that there could be several common causes, such as a tripped circuit breaker, a problem with the thermostat, or a faulty air handler motor. The air handler is the indoor unit of your HVAC system that circulates the air throughout your home. If it's not turning on, it could be preventing your entire system from functioning properly.
Some common symptoms of an air handler issue include no airflow coming from the vents, the system not responding to the thermostat, or strange noises coming from the unit. To troubleshoot, you'll want to check the circuit breaker, inspect the air filter, and make sure the thermostat is set correctly. If you can't identify and fix the problem, it's best to call in a professional HVAC technician to diagnose and repair the issue.