The "now" cost is inefficient cooling and heating with constantly running units that lead to increased utility costs. The "later" cost is replacement of equipment and the failure of the unit in a shortened lifespan.

Rooftop HVAC equipment has certain design limitations, and if not properly maintained the equipment will exceed its design limitations with the result being eventual failure.

Air conditioning equipment is designed to operate with a specific quantity of air passing over the indoor coil surface. When air filters are not replaced regularly, they become clogged and coated with dirt, as do the indoor coils. Dirty filters and indoor coils block a portion of the air flow causing the amount of air to drop below the specific design limits. Dirt leads to less efficiency, which leads to equipment break down and ultimately replacement.

Loose or broken drive belts cause similar problems to dirty filters. A loose drive belt will slip on a pulley, resulting in a less efficient drive. This wears out the groove in the pulley, so when the old belt is replaced, the new belt will also wear out quickly. Consider this: belts for $15 on a regular basis, or $300 for pulleys?

Cooling and condensation of the refrigerant vapor is designed to transfer heat. If the finned surfaces of the outdoor coils are dirty, the coil's ability to transfer heat dwindles. With the reduced ability to displace heat from the unit, the operating temperature and unit pressures increase. If that exceeds the manufacturer's safe limit, the unit will shut down. If it doesn't and the unit does not automatically shut down, it will continue to run at a reduced efficiency and increased rate of wear.

Electrical relays, contactors and bearings should also be serviced on a regular basis.