The answer to 'why is my HVAC system not turning on' is that there are several common causes, including a tripped circuit breaker, a faulty thermostat, or issues with the HVAC unit itself. If your HVAC system is not powering on, the first thing to check is the circuit breaker. Make sure it has not been tripped and reset it if necessary. You should also check the thermostat to ensure it is set correctly and the batteries are working. If those basic troubleshooting steps don't resolve the issue, there may be a problem with the HVAC unit that requires professional diagnosis and repair.
If you have tried resetting the circuit breaker and checking the thermostat, but the HVAC system still won't turn on, it's best to call an HVAC technician to inspect the system. They can diagnose the underlying issue and provide the necessary repairs. Attempting to fix complex HVAC problems without proper training and equipment can be dangerous and may lead to further damage to the system.