If you hear a strange noise coming from your air conditioning system, it’s a good idea to find the cause. It might be a minor issue or something signaling it’s time for a replacement. Here are the common AC sounds you may hear and what each of them likely means.
Rattling, Banging or Thumping Noise
A rattling sound could mean various things depending on where you’re hearing it. If you can hear it all over your house, it’s likely that either your ductwork was improperly installed or a section of it has become loose.
When you start hearing this sound, make sure all your vents are open. Closed vents can cause ducts to spring a leak or become loose due to pressure differences.
If the sound is coming from the condenser unit (the big box in your backyard), it might be that a part has come loose and is getting blown around. It could also be a small branch or other debris that got stuck inside the unit. You can shut off power to the condenser at the breaker box and then look in it to see if you can spot the problem.
A buzzing noise means you probably have an electrical issue. It could be the contactor relay switch, the condenser fan motor or a loose wire. Another possibility is that your AC is frozen because ice has formed inside.
A hissing noise means either a line or coil is leaking refrigerant. You need a licensed professional to fix this as soon as possible as refrigerant is expensive and needed by your AC system to operate correctly. Refrigerant is also poisonous.
Your AC system will click whenever it’s turned on or off. If you hear a loud clicking noise when it’s running, though, there’s an electrical issue, such as with the electrical controls, a thermostat or the relay. An AC technician can solve this problem and prevent further damage.
The compressor can make a grinding noise when it’s become worn down. The sound is caused by the compression of refrigerant, which shouldn’t happen when the appliance is running correctly. This noise is a sign you need a new compressor.
A grinding sound can also be caused by the fan belt. The belt has come loose and needs to be either put back in place or replaced before it causes damage to other parts.
Older air conditioners made a clunking sound when their motor needed to be lubricated. Modern air conditioners don’t have this issue. It’s best to have an HVAC professional lubricate the motor as high-voltage systems are involved.
High-Pitched Squealing Noise
This noise means it’s likely the compressor is damaged. High internal pressure has built up inside it, although compressors have a sensor designed to shut things down should pressure build too high. You should turn your AC off right away and call a professional.
Low-Pitch Squealing Noise
This sound means the belt in your outside AC unit needs to be replaced. A technician can replace a worn belt quickly and easily. You should schedule one to do so before the belt snaps and your air conditioning system shuts down.
A humming noise usually means there’s a minor problem that needs attention. It likely means there’s a loose part or pipe that is vibrating when the AC system is on. You should have a licensed technician look into the sound before it leads to a more serious problem.
If the compressor won’t start and makes a humming sound, the problem is probably the motor. The issue could also be there’s a loose wire somewhere.
This is the noise of something stuck in the blower blades. The object should be cleared away from the blades before it causes wear and tear.
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