Rooftop Unit Service & Replacement — Duluth, Superior & the Twin Ports

What is an economizer and why does it fail here?

An economizer is a damper assembly that brings in outdoor air for free cooling when conditions allow, instead of running the compressor. In a climate with as many cool hours as ours, a working economizer can handle a very large share of the annual cooling load at essentially no compressor cost.

They fail constantly and silently. Actuators burn out, linkages seize, outdoor air and return air sensors drift or fail, and the damper ends up stuck — either closed, in which case you run compressors on a 55°F day for no reason, or open, in which case you are heating outdoor air all winter and wondering why the gas bill is what it is. A stuck-open economizer in January is one of the most expensive faults a Twin Ports building can have, and from inside the building it is invisible.

We test economizer operation on every maintenance visit: actuator stroke, damper travel, sensor calibration and the changeover sequence. It is unglamorous work and it is frequently the single highest-return item on a commercial building's HVAC.

What our weather does to rooftop equipment

Corrosion first. Salt-laden air off Lake Superior, winter road salt lifted onto low roofs, and constant freeze-thaw take cabinets, fasteners, coil fins and drain pans apart faster than inland equipment. We inspect cabinet integrity and coil condition and flag corrosion while it is still a repair rather than a replacement.

Condensate freezing. A drain that works in shoulder season freezes in deep winter, backs up, and floods a curb or a ceiling below. Proper trap design, routing and heat trace where needed prevents a claim.

Snow and ice. Drifting snow blocks intake hoods and condenser coils; roof-edge ice damages panels and hoods. Where a unit has a recurring problem, the answer is usually repositioning or shielding rather than clearing it every February.

Belts, bearings and motors take the freeze-thaw and the start-stop cycling hard. These are inexpensive parts on a scheduled replacement and expensive failures when they let go on the hottest or coldest day.

Curbs and roof penetrations. An aging curb gasket leaks water into the building and conditioned air out of it. On a replacement, curb condition and adapter design are a large part of doing the job properly — a new unit dropped on a bad curb is a leak waiting to happen.

Replacement: curb, crane, and keeping the space open

Two things decide the cost and complexity of an RTU replacement beyond the unit itself: whether the new unit fits the existing curb, and how hard it is to get a crane to the roof.

Curb compatibility is rarely perfect across manufacturers or generations, so an adapter curb is common and needs to be right — it carries the unit, seals the roof penetration, and transitions the supply and return duct. Done badly it leaks air and water for the life of the unit.

Crane access in downtown Duluth and Superior can be genuinely constrained: narrow streets, overhead lines, parking and permitting, and hillside sites where the roof is not where the truck can reach. We survey the pick before quoting, so a crane does not arrive to discover it cannot make the lift.

We schedule picks outside your business hours and sequence the work so the space is conditioned again the same day wherever possible.