The answer to 'my duct cleaning won't turn on' is that there could be several common causes, such as a tripped circuit breaker, a faulty power switch, or a problem with the duct cleaning unit itself. First, check the circuit breaker to ensure it hasn't been tripped, and reset it if needed. If the breaker keeps tripping, there may be an electrical issue that requires a professional HVAC technician to diagnose and repair.
Next, inspect the power switch on the duct cleaning unit. Make sure it is in the 'on' position and that the connections are secure. If the switch appears damaged or worn, you may need to replace it. However, if you're not comfortable working with electrical components, it's best to call a professional HVAC technician to handle the repair.