Squealing usually means a worn blower motor bearing. Grinding means a motor is failing. Banging or clanking means something has come loose inside. Rapid clicking at startup points to a relay or capacitor. Buzzing is usually electrical. Hissing suggests a refrigerant leak. Grinding, banging and hissing warrant shutting the system off.
Typically a worn bearing in the blower motor, or on older equipment a slipping belt. Not an emergency, but it is the sound of a part wearing out. Getting it handled before it seizes is cheaper than after.
Metal on metal. A motor bearing has failed and the motor is destroying itself. Shut the system off. Continuing to run it usually turns a motor replacement into a motor plus whatever else it damages.
Something is loose, broken, or making contact with something it should not, often a fan blade or a component inside the compressor. Shut it off and call. This is the noise most likely to end in a destroyed compressor.
The system is trying to start and failing, usually a relay or a failing capacitor. Capacitors are one of the more common and more affordable failures we replace. Left alone, the repeated start attempts stress the compressor.
Generally electrical: a contactor, a loose connection, or a motor drawing current without turning. Sometimes it is just loose panel screws vibrating, which is harmless. Because the causes range from trivial to a genuine fire risk, it is worth having looked at.
Hissing often means refrigerant escaping. Bubbling or gurgling can mean refrigerant with air in the line. Either way you have a leak, and running low on refrigerant risks the compressor.
The short version: squealing, clicking and buzzing mean book a visit soon. Grinding, banging and hissing mean turn it off now. The cost difference between calling at the first noise and calling after the compressor fails is usually thousands.
A click when the system starts and stops, a low steady whoosh of air, and a brief whir as the outdoor fan spins up are all fine. So is occasional water dripping or trickling at the indoor unit, which is just condensate going where it should. What matters is a new noise, or one getting louder.
Common Questions
Yes. Grinding usually means a motor bearing has failed and the motor is damaging itself. Running it further typically increases the repair cost, and can take out neighbouring components. Shut it down and have it looked at.
Rapid clicking at startup normally points to a failing capacitor or a relay problem. The system is attempting to start and failing. Capacitors are among the cheaper components to replace, but repeated failed starts put strain on the compressor, so it is worth addressing quickly.
Hissing often indicates escaping refrigerant. It is not usually an immediate safety hazard in a home, but running a system that is low on refrigerant risks damaging the compressor, which is the most expensive part to replace. It also means there is a leak that needs locating.
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