If your air conditioning unit is making a loud booming or popping noise even when it's turned off and disconnected from the fuse box, there could be a few potential reasons:
Pressure equalization: Air conditioning systems have pressure equalization mechanisms that allow for the release of built-up pressure when the system is turned off. This pressure release can sometimes result in a loud booming or popping noise. It's a normal occurrence and generally nothing to be concerned about.
Temperature changes: When the air conditioning unit cools down, various components such as the metal housing, ductwork, or other parts may contract. This contraction can produce popping or creaking sounds as the materials adjust to the temperature change. Again, this is typically not a cause for concern.
Debris or foreign objects: It's possible that debris, leaves, or other foreign objects have entered the air conditioning system and are causing the noise. Check the unit for any obstructions and clear them if necessary.
Mechanical issues: If the noise is persistent, loud, or accompanied by other problems when the AC is in use, there could be a mechanical issue within the system. It's recommended to contact a professional HVAC technician to diagnose and address the problem.
It's important to note that diagnosing the specific cause of the noise without a professional inspection can be challenging. If you have concerns about the noise or if it persists or worsens, it's best to seek the assistance of a qualified HVAC technician who can examine your AC unit and provide appropriate recommendations.