If an AC unit is humming but not turning on, it could indicate a few potential issues. Here are a few possible explanations:
Power supply issue: Check if the unit is receiving power. Ensure that it's properly plugged in and that the circuit breaker or fuse is not tripped. If the power supply seems fine, move on to the next possibilities.
Faulty capacitor: The capacitor in an AC unit provides a boost of energy to start the compressor and fan motors. If the capacitor is defective or worn out, the unit may emit a humming sound but fail to start. A professional HVAC technician can test the capacitor and replace it if necessary.
Motor problems: The humming could be due to a malfunctioning motor. The motor may be seized, preventing it from turning, or it could have a faulty start/run winding. This requires the expertise of a professional to diagnose and repair.
Faulty thermostat: The thermostat could be malfunctioning, preventing the AC unit from receiving the signal to turn on. Try replacing the batteries in the thermostat or resetting it to see if it resolves the issue.
Blocked or frozen components: If the unit's condenser coils or evaporator coils are dirty or blocked, it can cause the AC unit to overheat or freeze up. This can result in a humming sound without the system turning on. Regular maintenance and cleaning of the coils can help prevent this problem.
It's important to note that attempting to fix complex AC issues without proper knowledge and experience can be dangerous and may cause further damage. It is best to contact a licensed HVAC technician to inspect and repair your AC unit. They have the necessary expertise to diagnose the problem accurately and safely perform any needed repairs.