Roberts Mechanical repairs and services packaged rooftop units across Orlando and Central Florida for restaurants, retail, offices, warehouses, churches and light industrial buildings. We have worked on commercial mechanical systems from our east Orlando shop since 2006. A rooftop unit is a self-contained package, compressor, condenser, evaporator and blower all in one cabinet sitting on a curb, and the faults it develops are specific to that arrangement.

The economizer, and why your bill is high

Most commercial RTUs have an economizer, a set of motorised dampers that pull in outside air when it is cooler than the return air. In a northern climate it saves real money. In Central Florida it is useful for a few weeks a year and it is the single most neglected component on the roof.

When the actuator fails or the linkage seizes with the dampers stuck open, the unit spends July dragging in 92-degree, saturated outside air and trying to cool it. The building never quite holds temperature, the space feels humid, and the power bill climbs. Nothing makes a noise and nothing leaks, so it can run that way for years. It is the first thing we check on a rooftop complaint about high bills or humidity, and it is a repair, not a replacement.

Curb and flashing leaks

The unit sits on a curb, and the curb is flashed into the roof. When water shows up in the ceiling under a rooftop unit, it is roughly an even split between the condensate drain and the flashing, and the HVAC contractor and the roofer each tend to blame the other. We will tell you which one it is. Condensate on a rooftop also has to actually drain, and pans that have rusted through or drains that have been running uphill since the last changeout are common.

Belts, bearings and blower assemblies

Many RTUs still use belt-driven blowers rather than direct drive. Belts stretch and glaze, bearings dry out, and sheaves get misaligned, which shows up as reduced airflow, a squeal at startup, or vibration you can feel in the ceiling below. These are inexpensive parts and they are the ones a maintenance contract is genuinely worth having for.

Compressor staging

Larger rooftop units run two or more compressors or stages. When one stage fails, the unit still cools, just not enough on a hot afternoon. Staff report that the building is fine in the morning and unbearable by three o’clock, and it gets written off as the system being undersized. It is usually a failed contactor, capacitor or compressor on one circuit, and it is diagnosable in an hour.

Condenser coil fouling

A rooftop condenser lives in full sun, in the path of kitchen exhaust, roof dust and whatever the parking lot throws up. Coils foul faster up there than at ground level, and a fouled coil raises head pressure, kills capacity and eventually kills compressors. Cleaning is cheap. What it prevents is not.

Controls, thermostats and zoning

Inconsistent temperature across a building is more often a controls or zoning problem than an equipment problem. Before anyone quotes you a new unit for uneven cooling, the dampers, sensors and thermostat programming are worth eliminating.

Getting on the roof

Some contractors are slow to quote rooftop work because it needs proper access, fall protection and often a lift or crane for anything larger than a service call. We do this work routinely. If access to your roof is awkward, tell us when you call and we will plan for it rather than discovering it on the day.

Replacing a rooftop unit

When an RTU genuinely is finished, the curb is the detail that decides how the job goes. A new unit rarely matches the footprint of the one it replaces, so the choice is a curb adapter or a new curb, and that decision affects cost, roof penetration and how the flashing is rebuilt. Anyone quoting a rooftop changeout without discussing the curb has not looked at it properly.

Replacing rooftop equipment is permitted mechanical work, and the unit has to be anchored to resist Florida design wind loads. We pull the permit, coordinate the crane or lift, and handle the curb and flashing as part of the job rather than leaving it for someone else.

Before you approve a rooftop replacement

Rooftop units are where replacement quotes get written fastest, because the equipment is out of sight and the numbers are large. A stuck economizer, a fouled coil, a failed stage or a rusted drain pan all present as “the RTU is not keeping up.” All four are repairs.

Bring us the quote. We will diagnose the unit ourselves and give you three numbers: what the repair costs, how much life it realistically buys, and what replacement costs installed. Much of our work is on equipment another company already said was finished, which is the whole idea behind our second opinions.

Related services

• Commercial HVAC across Central Florida
• DOAS units and dedicated ventilation
• Cooling towers and air-cooled chillers
• Commercial refrigeration, including the walk-ins below the roof
• Ductwork services for distribution problems the RTU is being blamed for
• 24/7 emergency service

For emergency rooftop service call 407-405-2658. We will tell you honestly when we can be there rather than quoting a window we cannot hold.