Rooftop unit service and replacement for commercial buildings

Rooftop units, or RTUs, are packaged air conditioners built for commercial roofs. The compressor, both coils, the blower and the controls sit in one cabinet on a curb or stand, and the supply and return ducts drop straight through the roof into the space below. They are common on offices, storefronts and small commercial buildings because they keep the mechanical equipment out of the space the business uses.

Life on a South Florida roof is hard on them. They sit in full sun for most of the year, they run long hours to keep up with occupied spaces, and every storm season tests how well they're attached. Near the coast, salt air adds corrosion on top of that.

Service and diagnosis

When a rooftop unit stops keeping up, the diagnosis follows the same discipline as any air conditioner, applied to a larger cabinet with more going on: refrigerant pressures, electrical readings on the compressor, motors, capacitors and contactors, airflow across the coil, and the controls that tell the unit when to run. Many newer units also store fault codes or report to a building control system, and that history is often the fastest way to an intermittent problem.

The problems we find most on rooftop units are the ones the location causes:

• Electrical wear. Contactors, capacitors and fan motors working in rooftop heat for years.
• Refrigerant leaks. Often at corroded joints or coils, especially on buildings near salt air.
• Airflow problems. Clogged filters and coils, a worn belt or motor on the blower, and restrictions in the ducts below the roof.
• Drainage. Clogged condensate traps and drains that back water up into the unit or onto the roof.

The difference from a home is access. The work happens on the roof, in the weather, around edges and openings that need care, and that shapes how a service visit is planned.

Replacement

Replacing a rooftop unit is part air conditioning work and part logistics. The new unit has to fit the existing curb or stand, or an adapter has to bridge the difference. It has to match the building's electrical supply, carry the airflow the ducts below were built for, and be lifted onto the roof, usually by crane for larger units and taller buildings. In Broward it also has to be anchored to the structure under the High-Velocity Hurricane Zone rules, and that anchoring is checked at inspection.

Planning matters more on commercial jobs than residential ones. The lift may need a street permit or an early-morning slot, tenants need to know when the space will be without cooling, and the roof around a changed curb has to be sealed properly. Those details are worked out at the site visit, before the replacement is scheduled.

Sometimes the unit doesn't need replacing yet. A failed motor, a leak at an accessible joint or a control fault can be a sensible repair on a unit with life left in it. Sometimes an older unit with a failing compressor and a corroded coil is the better candidate for replacement. We lay out both paths and their trade-offs, and the owner or manager decides.

For general light commercial work, see commercial HVAC. Packaged units on homes and small buildings at ground level are covered under package units.