Weather and temperature changes cause compression and dilation of materials. A bi-annual service is required to counteract weather and temperature adverse actions.
When materials reach near their resistance limits A/C devices are going to brake. At this point, break downs are inevitable. They need to be replaced as soon as possible.
Maintenance is the process of verifying that your air conditioning is not in the verge of breaking. Twice a year visits are scheduled to check more than two dozen of points.