Air Filters
Evaporator and Condenser Coils
Fan Blades and Motors
Condensate Drain Lines
Ductwork
Grilles and Registers
Refrigerant Lines
Outdoor & Indoor Units
Thermostat
Refrigerant Leaks
Compressor Issues
Fan Motor Problems
Thermostat Malfunctions
Blower Motor Issues
Capacitor Failures
Electrical Problems
Condenser Coil Problems
Evaporator Coil Issues
Expansion Valve Problems
Ductwork Issues
Heat Exchanger Problems
Water Leaks
Control Board Issues
Airflow Problems
Rooftop unit installation, from the curb survey to the lift
Rooftop unit installation is a project with a crane in the middle of it, and almost everything that decides how that morning goes is settled weeks earlier, on your roof, with a tape measure. We measure the curb, the duct drop, the power and the gas, work out what the building and the lot can carry, plan the pick, and set the unit on the day that costs you least.
What has to be true before the crane is booked
A rooftop change-out is the largest single job in commercial HVAC, and the survey is where it is won or lost. Six items get measured on the roof, and none can be read off the old unit's model number.
The curb, and its condition
Outside dimensions, where the supply and return openings sit inside the frame, and the state of the rails and the wood nailer. A sound curb keeps a change-out to a lift instead of a roofing project.
The duct drop
How the supply and return duct meet the curb from underneath, whether those connections can be reached from inside the ceiling or only through the roof opening, and whether the duct will carry the air a current unit moves.
Power at the roof
Voltage and phase at the disconnect, the state of the disconnect and the whip after fifteen summers in the sun, and conductor size read against the new unit's data plate rather than the old one's.
Gas at the roof
Pipe size along the roof and how it is supported, the shutoff at the unit, and whether that run still holds pressure at full fire with everything else in the building burning.
The roof itself
Membrane type and age, drainage around the curb, and who holds the roof. That answer sets which trade cuts and flashes the opening, and it is settled long before the crane date.
The access route
Where a crane can legally and safely stand, what runs overhead, what the boom would swing across, where the old unit can land, and how the crew gets onto the roof.
All six are captured on one visit, because they interact. A curb that has to be rebuilt changes the roofing scope, which changes who is on site, which changes the hour the crane is booked.
Why a like-for-like swap is rarely like for like
Owners reasonably expect a swap: the old box off, a new one of the same tonnage on, home by dinner. Sometimes it is close to that. More often the new unit is a different shape from the one it replaces, and the difference has to be engineered before it is lifted.
Footprints move between generations
Cabinet lengths, widths and base rail positions change from one model generation to the next, and again between manufacturers, and the supply and return openings move within the base along with them. A curb framed in one decade rarely lines up with a unit built two decades later, even under the same nameplate.
Efficiency made the box bigger
Higher minimum efficiency is bought mostly with coil face area, and a larger coil needs a larger cabinet. Replacement units are commonly taller, longer and heavier than what they replace, which is a curb question, a structural question and a crane question at once.
The refrigerant is not the same
A new packaged unit is built for the refrigerant currently being made, not for whatever is in the machine you are removing. On a rooftop unit that costs nothing in field piping, because the circuit is sealed inside the one cabinet. It does mean the old charge is recovered and documented before anything is cut, and that nothing crosses over.
The hole in the deck cannot move
Everything on a roof is negotiable except the opening cut in the structural deck and the duct hanging under it. Moving that means framing, roofing and ceiling work inside a trading building, so the new unit gets reconciled to the opening instead. That is the job a curb adapter does.
What a curb adapter is, and what a bad one costs
An adapter is a fabricated frame made to two footprints at once. It sits on the existing curb, presents the new unit's base on top, and carries sheet metal inside it that takes the supply and the return from where they arrive out of the roof to where the new machine expects them. Ordinary work, when it is measured and drawn before the unit is ordered.
What goes wrong later is short and predictable, and every item on the list is cheap to prevent and expensive to reach. An adapter with no insulation sweats on a humid August day and drips through the ceiling below. A partition that is not sealed lets supply air short-circuit straight back into the return, so the unit runs and runs while the room never quite gets cold. Flashing stretched to a new height instead of remade to it holds until the first storm drives rain sideways, and then it is a leak no one connects to an installation from two years ago.
What we check on every adapter
- Insulated to the same standard as the curb, because the inside of it carries conditioned air across an outdoor space.
- Supply and return separated and sealed inside the frame, with the partition landing where both openings are actually cut.
- Set level and shimmed on the curb rails, so the unit's pan and bearings sit the way the manufacturer intended.
- Load carried on the adapter's structural rails down onto the curb rails, never on the sheet metal skirt.
- Flashing and counter-flashing remade to the new height by the building's roofer, with the gasket line continuous on all four sides.
Weight, the membrane, and where two trades meet
A rooftop unit is a machine sitting in the middle of someone else's waterproofing. That joint is where roof problems start, and it is worth knowing before the day who owns which side of it.
What the deck carries
Replacement units are often heavier than the ones they replace. Whether the deck, the framing and the curb take that increase is a structural question, answered from the building's drawings or by a licensed structural engineer. It is not answered by eye and we do not guess at it.
The crane asks the same question at ground level, since outriggers put concentrated load into a lot that may sit over a basement or a vault. Both answers are wanted before a date is booked.
Who cuts the membrane
Cutting, flashing and counter-flashing at a curb is roofing work sitting inside a mechanical job, so the building's roofer does it and we plan the day with them rather than around them. Where the roof carries a manufacturer's warranty there is a second reason, because the terms usually name who is permitted to touch the membrane.
A leak found in November is a much harder conversation when no one wrote down who was on the roof in June, which is why that goes in the record.
The crane, where it stands, and what has to be clear
Reach decides the crane as much as weight does. The machine has to make the lift at the radius it will actually work at, and that radius is set by where the truck can legally stand and how far the curb sits from the parapet. A load that is comfortable close in can sit at the edge of the chart out at the building.
Where it sets up
Firm, level ground with room to spread the outriggers, clear of anything below grade. Overhead is the other half of the same question: power lines, tree limbs, sign structures and the parapet all constrain where the boom can travel. On a restaurant roof the pick also has to clear the hood exhaust fans and the make-up air unit, planned alongside the rest of the restaurant HVAC.
What is closed, and by whom
The set-up area, the swing path and a landing area for the old unit are closed for the day, with nothing parked or stored in them. On a private lot we agree that area with you and the landlord. Where the machine has to occupy a street, a sidewalk or a fire lane, permission comes from the town or the village on their timetable.
Who calls the weather
The crane operator does, from the load chart for the machine and rigging in use, and a flat-sided cabinet on a hook catches more wind than owners expect. What we owe you is early warning, because your half of a lift day is staff, deliveries and a closed lot.
Every lift is drawn like this before the day: where the machine stands, what the boom crosses, where the old unit comes down, and which part of your lot is closed while the boom is up. Machine size and distances come from the crane company against your site.
Crane and rigging day planner
Eight stages, in the order they happen. Each tells you what has to be ready, who is on your site, what your building is doing, and the one thing that would stop the stage.
The lot, before first light
Ready
The agreed area cleared and coned, staff parking moved, deliveries pushed back, roof access unlocked, and the new unit staged where the boom can reach it.
On site
Our lead installer and your building contact. The crane has not turned into the lot yet.
Your building
Trading as normal, or closed if the lift falls on a closed day. Nothing is switched off yet.
What would stop it
A lot that is not clear. Cars belonging to people who are not answering their phones is the most common reason a lift day starts late.
The crane sets up
Ready
What the crew needs from the building: a named contact who can have a car moved, one door taken out of use, signage at the closed area, and somebody who can reach the tenants either side of you.
On site
The crane operator, a rigger and a signal person join our installers. The operator owns the machine and the lift plan from here on.
Your building
Still trading. Foot traffic and deliveries are routed around the closed area, and the route is walked with your staff, not just coned.
What would stop it
Ground that will not take the outriggers under load, or a below-grade structure nobody flagged. Both are survey items, and both stop the day at the gate rather than halfway through it.
The old unit is isolated
Ready
Somebody who can authorize a power interruption, and a short window agreed in advance with whoever it affects.
On site
Installers on the roof, one technician at the panel, the crane crew standing by.
Your building
This is where conditioning stops. On a roof running several units, only the zone this one serves.
What would stop it
A disconnect that cannot be locked out, or a circuit that feeds more than the unit. Both are what the survey is there to find first.
Refrigerant out, services broken
Ready
Recovery equipment and cylinders on the roof, the gas shutoff proved to hold, and access to the ceiling space below the duct connections.
On site
An EPA Section 608 certified technician does the recovery and records it. One installer works inside at the duct.
Your building
Nothing visible beyond noise on the roof and a ceiling tile out where the duct is released.
What would stop it
A gas shutoff that will not seat, which becomes a piping repair before the lift goes further. A system that has already leaked out changes the recovery, not the day.
The old unit comes off
Ready
Duct disconnected, curb fasteners out, rigging checked by the rigger, and the landing area empty with a clear route to it.
On site
Operator, rigger, signal person, installers on the roof, and one person whose only job is keeping the ground clear.
Your building
The exclusion zone is live. Nobody walks under the boom, including your own staff and anyone making a delivery.
What would stop it
A cabinet corroded through where the rigging has to attach. That changes the rigging plan on the spot, and it is the rigger's call.
The open curb and the adapter
Ready
The adapter fabricated to the survey dimensions and already on the roof, with insulation, gasket, sealant and a cover for the opening.
On site
Our installers set the adapter. The building's roofer works the membrane and the flashing, which is their trade and their scope.
Your building
The deck is open for part of this stage, which is why the space below is cleared and covered beforehand.
What would stop it
A curb worse underneath than it looked around the edges. Rot or corrosion is repaired before anything lands on it, and it is the usual reason a lift day runs long.
The new unit is set
Ready
The adapter sealed, level and shimmed, the gasket line continuous, and the crew positioned on the roof to guide the cabinet down onto the rails.
On site
Everybody. Nothing else happens on the site while this pick is in the air.
Your building
Still closed off below. The exclusion zone stays live until the boom is down and the hook is clear.
What would stop it
Weather, on the operator's call as above. Otherwise a gasket line that will not seat, which is corrected with the cabinet still on the hook instead of after it is bolted down.
Boom down, the lot reopens
Ready
The unit fastened down, the roofer's flashing and counter-flashing finished, the roof swept for debris and fasteners, and the old unit loaded out.
On site
The crane crew and the roofer leave. Our installers stay for the connections and the start-up that follow.
Your building
Parking comes back the same day. Conditioning returns when the unit is started, not when the crane leaves.
What would stop it
Nothing at this point. This is the end of the crane's day rather than the end of the job, and the two are worth keeping separate in your planning.
No durations here on purpose. How long each stage takes comes from the scope, from the crane company's plan for your site, and from the condition of what is found under the old unit. Your proposal names the window once the survey is done.
Power, gas and controls after the crane has gone
Power, gas and controls all get landed on a machine that has never run in this building. Each one meets something inherited, and the inherited half is what has to be proved rather than assumed.
Power
The feed is the part of the circuit that stays behind, so it gets proved: insulation condition where conductors have laid on a hot roof, the ground, and the state of the disconnect and the whip.
The whip is replaced where the new data plate calls for different protection, the disconnect stays within sight of the machine, and rotation is proved before the compressor is asked to turn.
Gas
The connection point on a new unit has almost always moved, so roof piping is extended or rerouted, supported off the membrane, and finished with a drip leg and a shutoff at the machine. Joints are leak tested before anything is fired.
Then the burner runs and manifold pressure is set to what the unit is actually receiving.
Controls
The wire in the curb was pulled for the old unit's control scheme, and on a change-out it is usually the limiting item. A staged unit needs conductors for what it actually does and a communicating control needs its own pair, so new cable through the curb is normal, not an extra.
Where the machine brings an outside air damper it is set up and proved on the day, and the building's exhaust and make-up air is balanced against it.
The two readings a change-out turns on
Rotation, safeties, static pressure, temperature rise and air balancing run on a change-out exactly as they do on new work, and the sequence is set out under commercial HVAC installation. Two of the readings behave differently when the machine is a packaged unit replacing another one, and those are the two below.
Charge verified, not topped off
A packaged unit arrives with a factory charge matched to the line lengths inside its own cabinet, so on most change-outs the charge is verified rather than added to. Verification is superheat and subcooling read together once the machine has settled.
The pair is what makes the reading useful. High superheat with low subcooling is a system short of refrigerant. High superheat with subcooling still healthy is a restriction between the condenser and the metering device: the same complaint at the compressor, a different fault, and subcooling is precisely what separates them.
The duct is the one that did not change
A current unit generally wants to move more air than the one it replaced, and the duct under the curb is the same duct it always was, so airflow on a change-out is read against an inherited system.
Where the readings say the duct is the limit, we say so instead of winding the blower up until the building is noisy and the coil is starved. That is a scope conversation before the invoice, and it is why the duct drop is measured at survey.
The old unit, the record, and the first service
Closing out is where a rooftop job is either documented or forgotten. The middle card is the one owners never ask for and need five years later.
Where the old unit goes
It leaves on the same crane visit and off the site the same day. A cabinet left on a roof for later is a load nobody accounted for and a hazard in the first storm, and it goes for scrap instead of into a corner of your lot.
The roof record
The start-up readings, the control settings, the filter sizes and the disconnect labeling, plus the part specific to a roof: what the adapter was made to, how the flashing was detailed, and who did the membrane work on the day.
Warranty and first service
Registration is filed at our end so the machine is on the manufacturer's books from the day it ran. Terms come from the manufacturer and differ by unit and by component, so what you get is the coverage for the machine you bought.
That roof page settles an argument years later, and it exists only if it is written while the roof is open. Coverage pays for parts that fail, not for a coil nobody has cleaned since the day it was set, which is why the first visit under a maintenance plan goes in the calendar at handover.
What owners ask before they sign
Four questions come up on almost every rooftop change-out, and none has a useful answer before somebody has been on the roof.
How long is our building without heating or cooling?
From the moment the old unit is isolated until the new one is started. That comes from the scope, not from a rule of thumb: a change-out onto a sound curb is a different day from one where the curb needs rebuilding. It is why lifts get booked before opening, overnight or on a closed day, and why on a roof running several units the work is phased so the whole building is never down at once.
Our building is leased. Who has to approve this?
On most leases the roof belongs to the landlord and the unit serving your space belongs to you, which splits a change-out across two signatures. The survey establishes who owns the curb, who holds the roof warranty, and whose roofer works the membrane. Those answers early are what keep a landlord from stopping a job with a crane already booked.
Our roof is near the end of its life. Should the two jobs be combined?
Ask your roofer before the unit is ordered. A change-out opens the deck, remakes the flashing and puts a crane on the lot, and a reroof does much of that again a year later. Where the two fall close together, sequencing them as one project saves opening the same detail twice. Where the roof has years left, nothing is gained by waiting.
Our unit still runs. How do we know it is time to replace it?
Age and condition against the cost of the repair in front of you, whether parts are still made for that model, and whether the refrigerant it runs on is still practical to buy. One expensive failure on a machine with years left is a repair, and we will say so. Units of the same vintage on one roof tend to reach the end within a few years of each other, which is worth knowing when you budget. Weighing one specific fault, start with rooftop unit repair.
Get the lift planned before you get a price
Every honest number for a rooftop change-out starts on the roof. We measure the curb, the duct, the power and the gas, work out what the deck and the lot allow, and come back with a scope you can hold beside anybody else's. Licensed and insured across Suffolk and Nassau County since 1999, with 24/7 emergency cover every day of the year and a technician typically on site inside 90 minutes.
Serving businesses across Suffolk and Nassau County. Unit down in the middle of a heat wave? That is emergency HVAC repair, answered around the clock.