The answer to 'my preventive maintenance won't turn on' is that there could be several common causes, such as a tripped circuit breaker, faulty thermostat, or issues with the HVAC unit itself. Symptoms may include the system not powering on, no airflow, or the thermostat not responding. To troubleshoot, first check the circuit breaker and reset it if tripped. Next, inspect the thermostat to ensure it's set properly and has working batteries. If those don't resolve the issue, there may be a problem with the HVAC unit that requires a professional technician to diagnose and repair.
Attempting to repair complex HVAC issues yourself is generally not recommended, as it can be dangerous and may cause further damage. It's best to call a licensed and insured HVAC technician who can properly identify and fix the problem.