Why does American Standard AC hum loudly when compressor engages?

 
Electrical Sources of Humming
 

• The compressor requires a significant surge of electrical power when it starts. This high inrush current generates strong electromagnetic fields in the motor windings, which can create an audible hum, as often noted by residents in St. Louis.
• Alternating current interacting with the motor components produces cyclic magnetic forces, making the compressor emit a continuous humming noise during operation.

 
Mechanical Vibrations and Resonance
 

• When the compressor engages, internal components such as the motor armature, pistons, and bearings begin to move and vibrate. These vibrations can resonate within the compressor’s structure, amplifying the sound.
• Any loose mounts or worn vibration-dampening parts can further exacerbate the noise by allowing even minor mechanical movements to produce significant audible vibrations.

 
Capacitor and Startup Concerns
 

• If the compressor’s start capacitor is failing or has degraded over time, it might not provide the necessary boost at startup. This can delay the proper rotation and synchronization of the motor, causing it to struggle and produce a louder humming noise.
• Such issues can force the motor components to work harder during startup, resulting in increased mechanical vibrations that translate into sound.

 
Design and Installation Factors
 

• The inherent design of the compressor and the materials used in its construction may not completely suppress the sounds generated during operation. Metal housings and internal mechanisms can act as sound amplifiers if not well insulated.
• Installation factors such as improper leveling, insufficient mounting, or inadequate sound insulation in the AC unit can allow the engine’s vibrations to become more pronounced, contributing to the loud AC hum when the compressor engages. This is a scenario frequently encountered in St. Louis properties.