ACHRNEWS

Preparing Rooftop Units for Summer Use

June 15, 2009
Bruce Anderson of CES Group, said that when installing units, such as this Mammoth® outdoor packaged DX rooftop a/c unit, “be sure to check the refrigerant/oil charge before starting the compressors to ensure no refrigerant escaped during transit or installation.”



You have sunscreen? Check. Sunglasses? Check. Bottles of water and/or other liquids to keep you hydrated in the heat? Check. OK, so you’re equipped, but are the rooftop units you install, service, and/or maintain ready for summer?

There isn’t a lot of work involved in the actual switching over of a rooftop unit from winter to summer use, but the units still call for attention.

Bruce Anderson, vp of marketing, CES Group Inc., Chaska, Minn., spoke about maintenance on a packaged rooftop air handler. He said, “Most of the commercial air handlers have few items in need of changeover. Oftentimes, the same handler is used for both heating and cooling. If the air handler is capable of heating and cooling, the DX or water chiller would be started to provide a cooling medium to the air handler.”

Paul Hollingsworth, manager of warranty service, Applied Air Handling Group, McQuay International, discussed maintenance for packaged rooftop units, and said, “With the advent of warmer weather conditions, the units will be required to work harder. This means it’s a good time to check over the unit to make sure airflow through the unit has not diminished and that refrigerant systems are fully charged.”



TIME FOR INSPECTION AND CLEANING

Switching over to summertime operation provides an excellent time to perform routine checks. Hollingsworth, Anderson, and Jim Wilenius, national service manager, Heat Controller, Jackson, Mich., all agree that inspecting, checking, and cleaning are a big part of this work.

“Any required maintenance should be performed at this time, which is key to reliable, long-term unit operation,” said Hollingsworth.

Wilenius, who discussed installing or servicing a package gas/electric or package cooling with electric heat unit in his answers, echoed that sentiment, saying, “At the beginning of each cooling season, the cooling section should be inspected and cleaned to ensure proper operation and efficiency.”

Both Anderson and Hollingsworth said one of the parts to check is the filters at that time. “Inspect pre and final filters and replace if necessary,” stated Anderson.” Hollingsworth said to “check filters as required to meet airflow requirements.”

They also recommend checking the cooling coils. Hollingsworth said to check them for blocked airflow. Anderson said for packaged rooftop air handlers to “Ensure the cooling coil is clean, per manufacturer’s recommendations. If the cooling coil was drained and filled with glycol freeze protection media, blow it out and ensure all air is vented from the coil and pipes.”

Drain pans, drain lines, etc. are parts that were suggested for inspection and cleaning by Wilenius and Hollingsworth. Wilenius said to “inspect the drain pan and condensate drain at the same time the evaporator coil is being checked and clean if necessary.” Hollingsworth said to “clean drain pans as necessary, check that drain lines are clean, and check that there are no cracks or leaks in the condensate trap that might interfere with drainage from the unit.”



Switching to summer use is a good occasion to check all filters on outdoor units, such as on this Temtrol® outdoor packaged air handler.

Hollingsworth noted various other parts of the units that should be routinely checked on a packaged rooftop unit when switching over from heating to cooling. They include:

• “Make sure that condensing coil fins are clean and free of debris.

• Check that all condensing fans are operating properly.

• Check belts for wear and replace as necessary.

• Check belt tension and alignment.

• Check that refrigerant operating points are where they should be.

• Check superheat settings on thermal expansion valves.

• Check subcooling from the condenser, which helps to confirm that the system is properly charged.
• Verify that the compressor crankcase heater is turning on and operating properly when the compressor turns off.

• Check the compressor crankcase heater’s amp draw.

• Check the economizer actuator to make sure it strokes smoothly through the entire range of motion.

• And, check controls and settings to make sure the economizer only operates when it is supposed to.

Wilenius said other maintenance work to be done on these units at the same time as inspecting and cleaning the evaporator coils, includes:

• The condenser fan motor and venturi should be inspected for obstructions.

• Take a look at the air circulation blower wheel and motor for any accumulation of lint, dirt, or other obstructions. Of course, clean the blower wheel if needed.

• Check the blower motor mounts and blower housing to make sure they’re not loose or that some other damage has occurred.
• Finally, check the electrical controls - compressor contactor, capacitors, time delays, etc. - for signs of wear, damage, or failure. If you find a problem, repair or replace the part now.

For packaged rooftop air handlers, Anderson said to inspect the following parts in order to prepare for the cooling season:

• Outdoor air dampers for correct outdoor air setting and that they are free from any obstructions;

• Energy recovery wheel drives and wheel cleanliness;

• Humidification system if present;

• Any UV light system; and

• Any variable-speed fan drive (VFD or Varicone actuators).

Also, Anderson said to “inspect and calibrate airflow monitoring sensors and tubing.”

Other service and maintenance work that should be done on this type of equipment, before using it for warm weather operation, stated Anderson, is:

• Check coil valve actuators for correct operation.

• Grease fan drive bearings and inspect/replace fan drive belts.

• Check for fan vibration caused by being out of balance.

• Balance the waterside and ensure correct water temperature rise through coil.


“At the beginning of each cooling season, the cooling section should be inspected and cleaned to ensure proper operation and efficiency,” said Jim Wilenius of Heat Controller.

WHEN INSTALLING

Wilenius said that when installing or servicing a package gas/electric or package cooling with an electric heat unit, there are a few things that should be done for cooling operation.

“Assure that the system is cooling properly, check the compressor (or compressors) for correct voltage and running current limits. You want to make sure the condenser fans and indoor air blower are running free and quietly. And, of course, check for temperature differential across the supply and return to ensure that proper cooling is occurring. Also, check airflow at the duct outlets to see that the blower speed (cfm) is correct.”



When switching over a packaged rooftop unit from heating to cooling, Paul Hollingsworth of McQuay International, said to “make sure that condensing coil fins are clean and free of debris.”

Anderson, speaking about packaged rooftop air handlers, recommended the following for new installations:

• “Check filter cleanliness if the unit was operated during construction. Ensure there is no bypass around filters.

• Air balance the system. Be sure not to exceed the manufacturer’s cooling coil face velocities to not promote condensate carryover past the drain pan and down the ductwork.

• Ensure drain trap from cooling coil drain pan is sized properly for airflow and pressure drops.

• Ensure gasket sections and insulation of d-mount sections are secure with no air leaks or exposed cold surfaces, which can cause units to sweat.

• Ensure all safety guards/shields and grates are in place and secure.

• Unwanted sweating of the unit can occur when cold interior surfaces come in contact with hot, humid air. Be sure these surfaces are properly insulated and thermal breaks used.”

He also counsels that technicians “always follow [the equipment] manufacturer’s installation, operation, and maintenance and service recommendations and schedule.”

This last bit of advice is good for all installation and service technicians to adhere to no matter the type of equipment whether an industrial, commercial, or residential HVAC unit or refrigeration equipment.

Publication date: 06/15/2009