A new sound from your air conditioner is the system telling you something. Some noises are a quick DIY check; others mean shut it off and call a tech before a small problem becomes a compressor. Here is how to read each one.
A hum with the fan or compressor refusing to start usually points to a failing run capacitor - the most common summer failure in North Texas. The motor is drawing power but has no "kick" to start. This is a routine, inexpensive repair, but running the system in this state can burn out the motor, so it is worth a prompt call rather than a wait.
A loud bang or clank from the outdoor unit typically means a loose or broken component inside the compressor, or a failed part knocking around. Turn the system off at the thermostat and call. Continuing to run a compressor making this sound risks turning a repair into a full compressor replacement.
Squealing usually comes from a worn blower belt (on older belt-drive systems) or a motor bearing starting to fail. On modern direct-drive systems it is almost always a bearing. It is not an emergency, but it will get worse, and a seized bearing takes the motor with it - so book a visit before it escalates.
A single click when the system starts up and another when it shuts down is completely normal - that is the contactor and relay doing their job. Constant or rapid clicking while running is the warning sign, and it points to a failing relay, control board, or a thermostat issue. If the system is also short-cycling, have it looked at.
A grinding sound means metal on metal - almost always motor bearings that have failed. Shut the system off. Running a motor with failed bearings will destroy it quickly, and a $200 bearing problem becomes a motor replacement. This one is a call-a-pro, not a wait-and-see.
A hiss or a bubbling sound often signals a refrigerant leak. Beyond the cooling problem it causes, refrigerant is a regulated substance the U.S. EPA restricts, and a leak has to be found and repaired by a licensed tech, not just topped off. If you hear hissing along with weak cooling, call promptly - the sooner the leak is sealed, the less refrigerant is lost and the smaller the repair.
Rattling is the most benign of the group and the most DIY-friendly. It is often loose screws on a service panel, a stick or debris in the outdoor fan, or a cover vibrating. With the system off at the breaker, it is safe to clear leaves and debris from the outdoor unit and check that the panels are seated. If the rattle continues after that, something internal is loose and worth a look.
Banging, grinding, and hissing on a 100-degree Lewisville afternoon are the sounds to act on fast - each can cascade into a compressor or refrigerant failure if the system keeps running. Shut it down and call. For after-hours no-cooling, see our emergency AC repair page.
If a noise has you worried, do not guess with a compressor on the line. Call 817-725-9234 or request service online. Related: Why is my AC not cooling and AC repair services.
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