All air-conditioning units must be grounded electrically to

Prevent electrical shock

Grounding is a non current carrying conductor mainly used to guard against hazards due to leakage in electric circuits

Explanation:

The grounding refers to the connection of an electrical equipment exposed metallic parts to the ground to serve as a source of current flow in the event of an insulation failure will cause the fuses to trip thereby isolating or removing electric power from the device

Grounding also prevents the accumulation of static electricity which can be a source of fire in inflammable areas.