Rooftop units have evolved and improved dramatically since first being introduced. The units now have high-tech controls and diagnostics, easier access to frequently serviced parts, and multiple innovations to improve IAQ. These improvements, when combined with regularly scheduled maintenance, can produce years of reliable performance and indoor comfort.

A light commercial package rooftop unit should be serviced regularly. Both quarterly and semiannual services are common, although monthly service, while extreme, also has a place, especially in critical applications. Regular maintenance should take place at the start of the heating season and again at the start of the cooling season. Filter maintenance, depending on the equipment application and filter type, may need to be performed on a more frequent monthly basis.

USING A CHECKLIST

Many items that are part of a routine HVAC system maintenance inspection have remained constants over the years. However, evolving technology designs and changing environmental laws have resulted in adjustments and additions to the inspection process. The checklist that follows is a blend of previously established procedures and the new methods employed in maintenance inspections.

Speak to the building owners and occupants and develop a written record of any reoccurring or nuisance system problems identified. Discuss the space comfort to piece together the operating history of the unit.

Disconnect the electrical power to any HVAC equipment prior to performing service or maintenance. Shut off the unit at the service disconnect switch or main electrical distribution panel. If at all possible, arrange for a licensed electrician to install a weather-tight disconnect.

Clean or replace the air filters on a consistent basis.

Inspect the fan motor. Also, check both the pulley and belt on belt-driven units. If the belt is loose it can add wear to the pulley, reduce fan speed, and ultimately freeze the coil. Remove the fan belt and check the motor and blower bearings to be sure they are securely mounted and rotate easily and quietly. Then check the condition of the fan itself. Does the fan operate smoothly and quietly? A fan that's plugged up with dirt will reduce airflow. Defective motors and damaged fan blades should be replaced.

Inspect the belt and drive system and replace the belt if it is worn or cracked. Belts should be properly adjusted for tightness using a belt tension gauge. Loose belts will squeal and result in excessive belt and pulley wear. Excessively tight belts can result in premature damage to the blower bearings and mounts.

Inspect and periodically clean the evaporator coil using a hand pump garden sprayer containing a mixture of a nonacidic cleaner and water.

Test the economizer itself for proper operation, checking the linkage for binding, full stroke actuator operation and the proper functioning of the economizer limiting thermostats, including the mixed air thermostat, the enthalpy control, outdoor dry bulb control, and minimum outside air potentiometer.

Inspect the condensate drain and clean it, if necessary. An unclean drain can clog and leak condensate through the unit base pan onto the floor below. Mold and mildew are also a concern for any standing water in the drain pan, in the base of the unit or in the unit insulation.

Stop, look, and listen. Take a few minutes to visually scan the unit for anything that does not appear to be normal. Check to be sure barometric exhaust dampers are not stuck in the closed or fully open position. Inspect all outdoor fan motors to be sure they are operating as intended. Be certain that electrical wiring is properly secured and away from spinning fan blades. Inspect refrigerant piping for lines rubbing together. Noise and vibration are very good indicators of a potential problem. Listen and/or feel for any unusual bearing noises, belt squealing, rattles, humming or buzzing that would be an indicator of a mechanical problem.

Inspect the blower wheel and clean it if necessary. A dirt-filled blower wheel can reduce system evaporator airflow by as much as 35 percent.

Inspect, clean, and lubricate the economizer damper blades, bushings, linkage, and gaskets for a proper seal to ensure the appropriate amount of air for air balance.

On units with smart control modules, consult the manufacturer's operating manual on how to download equipment lockout information from the module. Newer systems retain the most recent equipment lockout information in the memory of the module. This information is extremely useful in determining the source of any nuisance lockouts with the individual circuits of the system.

Periodically clean the condenser coil using a hand pump garden sprayer containing only a mixture of nonacidic coil cleaner and water.

Inspect the cabinet for obvious damage, deterioration and signs of rainwater entry. Any sources of rainwater entry should be permanently repaired with gasketing or silicone-based caulk. Always replace all missing access panel screws.

A light commercial package rooftop unit should be serviced regularly. Both quarterly and semiannual services are common, although monthly service, while extreme, also has a place, especially in critical applications.

Inspect the unit mounting supports to ensure quiet operation. Use cork/rubber gasketing to eliminate metal-to-metal vibration transmission.

Inspect duct connections for air leaks, recirculation, and damage.

Inspect the electrical compartment for signs of wear or overheated wires, contactors, or loose terminal connections. Loose connections can result in serious damage to the compressor.

Remember that replacing a contactor is easier and much less expensive than replacing a compressor.

Functionally inspect the unit's safety components, such as the high-limit switch, and test them using the manufacturer's guidelines.

Check the refrigerant charge using the manufacturer's guidelines.

Inspect and record the amperages of the primary system components and verify that they are within the published limitations that appear on the unit data label and in the manufacturer's instructions.

Functionally inspect the heating components to ensure proper operation and firing rates on gas-fired equipment. Inspect the flue and burner components for excessive sooting.

Clean out debris that may have accumulated in the unit. Visually inspect a unit's coils, and ensure that nothing is blocking the condenser side airflow. In addition, check the P-trap. It may have dried out and cracked, which can lead to leaks, or simply have been broken off. An improperly functioning P-trap does not drain properly, an especially important point during the cooling season.

Finally, be sure to discuss with the business owner any findings that indicate potential problems and put an action plan together to correct the situation.

Walt Jacobe is the commercial marketing manager at York, a Johnson Controls Co. He can be contacted at 405-419-6546 or at walt.jacobe@york.com.

Publication date: 06/19/2006