What must be done periodically to maintain an A/C system's effectiveness?

Maintaining an A/C system's effectiveness requires a range of actions to ensure optimal performance, energy efficiency, and longevity of the unit. Each of the listed tasks plays a vital role.

Regularly cleaning the condenser coil is crucial because the coil dissipates heat from the refrigerant. If it becomes dirty or obstructed, the system has to work harder to release this heat, which can lead to decreased efficiency and potential overheating.

Changing the air filter is another essential task. A clean air filter allows for better airflow, which is necessary for the system to properly cool the air in a space. A clogged filter can hinder airflow, straining the system and reducing its effectiveness, potentially leading to mechanical failures.

While increasing refrigerant levels might be necessary under certain conditions – such as if there’s a leak – routine maintenance usually focuses on preventive measures like cleaning and replacing filters to ensure that the system operates smoothly without needing to adjust refrigerant levels frequently.

Therefore, since all these tasks contribute to the maintenance and effectiveness of an A/C system, performing them periodically is a comprehensive approach to ensure the system runs efficiently, making "All of the above" the correct answer.