A popping sound in a central air conditioner may be the result of air expansion and contraction, dirty air ducts or issues with the blower. Older air conditioners are often louder than newer models and may require cleaning and replacement of worn parts to stop the noise.
Popping noises caused by expansion and contraction of air ducts is generally harmless, but owners can eliminate this noise by making a small dent in the air duct. Air conditioners with dirty ducts require cleaning to eliminate the popping noise, as do older models. Popping noises caused by a slipping motor belt or a loose part in the blower mechanism can be stopped by replacing the belt and other worn parts inside the blower.