Many municipalities have noise laws to protect you from excessive noise. Usually your public works department enforces these laws. They will visit your house and use a sound meter to measure the noise levels from the locations of your complaint - usually your back patio or bedroom. They will then advise the neighbor of the complaint and will offer solutions to help solve the problem. Different municipalities will have varying levels of acceptable noise. If you live close to traffic, airports or industry, then the permissible noise levels may be higher.
The remedies include; moving the air conditioner to a different location, replacing the air conditioner with a quieter one, installing noise reduction devices like ours, or to build a wall or barrier to reduce the noise transmission. The neighbor will be given an appropriate amount of time to resolve the problem before any penalties are imposed.