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
Commercial HVAC repair, from the symptom to the part that caused it
Commercial HVAC repair is a diagnostic job before it is a parts job: a space that will not hold temperature, a unit short cycling on its own safety, a breaker that opens on start, or a rooftop that has simply stopped. We diagnose and repair packaged rooftop units, split and multi-split systems, zoned duct systems and PTACs for Long Island businesses, tracing the fault to its cause before a part is changed.
Five families of fault, and how one turns into the next
Most of what we are called out to began somewhere else in the machine and worked its way through it. A condenser packed with cottonwood seed and roof grit raises head pressure. High head pressure heats the compressor. The compressor's internal overload opens to protect it. The owner reports a rooftop unit that runs and then stops. One cause, four ways of describing it, and only one of them is worth spending money on.
Faults sort into five families: airflow, the refrigeration circuit, the electrical side, the controls, and the gas heat section. Each has its own cheap check and its own expensive mistake, and on a gauge set each one imitates the others, which is why sorting a fault into the right family comes before touching a part.
The gas heat section shares a cabinet with the cooling on most commercial units and almost never shares a cause with it.
Come in from the symptom, or from the part you suspect
Two ways in. Choose what the building is doing and you get the parts that produce it, ranked the way a technician rules them out. Choose a part and you get what is measured on it, in what order, and what it gets confused with.
What is the building doing?
Which part do you suspect?
Cooling runs, the space never gets there
- Condenser fouled, a fan stopped, or the coil taking back its own discharge air
- Airflow down: loaded filters, a slipping belt, a dirty blower wheel
- Charge low from a leak, or a restricted metering device
- Economizer damper failed in the wrong position, so the coil is fed the wrong air
- Compressor worn and no longer pumping to specification
Condenser airflow and head pressure, then the temperature drop across the evaporator. Those two readings separate an air-side fault from a refrigerant-side one.
Short cycling, or tripping on start
- Compressor overload opening on heat from high head pressure
- Contactor pitted or welded, or a run capacitor low on capacitance
- A pressure safety cutting out and resetting itself
- Thermostat or sensor sited badly, satisfying before the room does
Which device is opening, and whether the compressor draws locked rotor amps. A unit tripping the building breaker and one tripping its own internal overload are different repairs.
Nothing runs at all
- Breaker open, or one fuse gone in a three-phase disconnect
- Control transformer failed, often with a shorted low-voltage wire
- A safety holding the circuit open: high pressure lockout, condensate float switch, heat section limit
- Thermostat or building management system not calling, or a schedule holding it off
Line voltage at the disconnect, then control voltage at the board. A large share of these calls end at a float switch or a fuse.
Weak airflow, or one area starved
- Filters loaded, or the wrong filter for the rack
- Belt slipping, glazed or broken, or a sheave set wrong for the duct
- Blower wheel caked, so the blades no longer bite the air
- Evaporator fouled on the entering side, where nobody looks
- Zone damper failed shut, duct crushed above a ceiling, or a return blocked with stock
Static pressure across the filter rack and the coil, then belt condition and tension. Tension is the check most often left out of a service, and it sets how much air the blower actually delivers.
No heat from the gas section
- Igniter open, or a flame sensor coated so the board drops the flame
- Pressure switch not proving: a weak inducer, a blocked flue, water in the sensing hose
- Gas valve or its wiring, or low manifold pressure at the burner
- Rollout or limit tripped, which is an airflow or flue problem rather than something to reset
- Heat exchanger cracked, which is a shutdown, not a repair
Whether the unit completes its sequence: call, inducer, pressure proved, igniter, valve, flame held. The step it stops on names the part.
Water where it should not be
- Drain trap missing, dry, or too shallow for the blower behind it
- Drain line blocked with biofilm, or pitched back toward the unit
- Pan corroded through, or left out of level after a coil clean
- Curb flashing or a cabinet seam letting weather in, which looks the same from below
The trap and the pitch. A pan on the suction side of the blower needs a trap deeper than the negative pressure the fan pulls, or water sits in the pan while the line stays dry.
Compressor and its protection
Commercial compressors rarely die of age. They die of heat, of liquid coming back down the suction line, or of a supply problem, and one that keeps tripping its own protection is reporting a fault elsewhere.
- Windings to ground, and resistance leg to leg
- Running amps on every leg against the data plate
- Pressures with superheat and subcooling
- What the protection device is responding to, before anything is replaced
A contactor that never pulled in, and a capacitor too weak to start the motor. Both are cheap, and from the ground both look like a dead compressor.
Contactor and capacitors
The parts most often at fault on a unit that hums, buzzes or does nothing. Contacts pit and weld from the arc of every start, coils weaken, and run capacitors lose capacitance quietly.
- Contact condition, and whether the coil pulls in on a call
- Measured capacitance against the rating stamped on the can
- Control voltage at the coil under load, not at rest
- Motor amps once it does start
Capacitance alone can pass a part that still fails the motor. A weakened run capacitor turns a compressor in April and will not turn it against high head pressure on a hot roof in August, so start and run amps are measured under real running conditions, not capacitance on a meter alone.
Condenser coil and fans
The condenser rejects the heat the building put into the refrigerant. It cannot do that through cottonwood seed, roof grit, kitchen grease or a corroded fin pack, and much of what fails downstream starts here.
- Fin condition through the depth of the coil, not only at the face
- Fan rotation, blade condition and amps on each motor
- The discharge air path, and any recirculation back into the coil
- Head pressure once the coil is actually clean
From the inside out, against the airflow, so the dirt leaves the way it came in. Rinsing the face drives it deeper into the fins and the coil measures worse afterwards.
Evaporator, metering and condensate
Where heat leaves the building's air, and where the water that comes with it has to go. The coil fouls on the entering side, ices when airflow drops, and is fed badly when an expansion valve or its bulb is not doing its job.
- The entering side of the fin pack, which means opening the section
- Temperature drop across the coil, and superheat at the outlet
- Sensing bulb contact, position and insulation on an expansion valve system
- Trap depth against blower static pressure, drain pitch, and whether the float switch works
An expansion valve is condemned far more often than it fails. A bulb that has slipped off the suction line reads air instead of pipe and drives the valve wide open, and a clamp puts it right.
Refrigerant charge and leaks
Systems do not consume refrigerant. A charge that is down has gone somewhere: a line rubbing inside the cabinet, a Schrader core, a braze joint, or a coil corroding from the outside in. Finding it is the repair.
- Superheat and subcooling read together, never one without the other
- Electronic leak detection over the likely joints and coil returns
- A nitrogen pressure test where a system has lost everything and shows nothing
- Recovery, repair, evacuation, then weighing the charge in
High superheat with low subcooling is an undercharge. High superheat with normal or high subcooling is a restriction, because liquid stacks up ahead of the blockage. Subcooling is what separates them.
Blower, belt and filters
The supply side. Most commercial blowers are belt driven, which gives an adjustable sheave to set airflow to the duct system and a wear part that gets no attention until it snaps.
- Filter condition, and whether it is the filter the rack was built for
- Belt tension, glazing, cracking and pulley alignment
- Blower wheel cleanliness, blade by blade
- Motor amps, bearing condition and static pressure across the system
The wheel. Dirt packed between the blades changes their shape, and no filter change recovers the airflow that costs.
Economizer and dampers
Free cooling when outside air is cool and dry enough to use, and a large hole in the building when it fails. Actuators seize, linkages work loose and changeover sensors drift, and because nothing alarms when they do, the fault runs on unreported.
- The actuator driven through its full stroke, both directions
- Linkage, blade travel and blade seals
- The changeover sensor and the setpoint it works to
- Minimum position against the outside air the space needs
Poor performance and a climbing bill with no fault code anywhere. The diagnosis is a damper driven through its stroke by hand, and the repair is mechanical rather than refrigeration.
Controls, thermostat and BMS
Setpoints, schedules, sensors and whatever the building runs above them. On larger and multi-tenant sites the unit takes its orders from a building management system, and equipment reported as broken is regularly doing what it was told.
- What the thermostat or the head end is calling for right now
- Sensor location and accuracy against a reading taken in the space
- Staging, minimum run times and any active lockout
- Low-voltage wiring and the control transformer feeding all of it
Before equipment is blamed, the sensor position is checked. Sun on the wall behind it, or warm air drifting off a copier, is enough to hold a whole floor out of range.
This is a starting point, not a diagnosis. Two identical rooftop units with the same complaint fail for different reasons, and the readings taken on the day decide which one you have. Some faults belong to a machine rather than to a symptom: a kitchen that will not clear, a building exhaust fan that has stopped, and duct that is the reason for the complaint.
Why the order of a diagnosis decides the bill
Every reading a technician takes is distorted by the fault upstream of it. Gauges on a system with a blocked condenser describe the blockage, not the charge. A temperature split measured with a slipping belt describes the belt. So the sequence runs from cheap to expensive and from the air side inward, one stage at a time.
Power, then safeties
Line voltage at the disconnect, control voltage at the board, and whether anything is already locked out. A unit sitting on a high pressure lockout has told you where to look before a single panel comes off.
Watch it run
What turns and what does not, what is iced, what is filthy, what smells hot, what the unit does when the call is made and dropped. Two minutes of watching removes several possibilities for free.
The air side
Filters, belt, wheel, both coils, dampers and static pressure. Everything measured after this stage depends on airflow being correct, so a fouled coil gets cleaned here, not written up for later.
The electrical side
Amp draws on each leg, capacitance, contactor condition and motor behavior against the data plate. A large share of single-visit repairs are decided here, and so is whether a compressor is worth testing further.
The refrigeration circuit last
Pressures converted to saturation temperature, superheat, subcooling, and a leak search when the charge is down. By this point the numbers describe the sealed system rather than the dirt in front of it.
The order matters at the end as much as the start: a new compressor put back into the conditions that killed the last one fails the same way. When a sealed-system part is condemned, the reason it died is corrected on the same visit.
What a lost leg does to a compressor
Most commercial equipment runs on three-phase power, and the motors in it depend on all three legs arriving balanced. When that stops being true, the damage is quiet, fast and usually blamed on the wrong part.
A three-phase motor that loses one leg while it is already turning does not stop. It keeps running on the two legs it still has, draws far more current through them, and heats until an overload opens or the windings give up. A motor that has not yet started simply hums and stalls, pulling locked rotor current the whole time it sits there.
The cause is rarely inside the unit. It is a blown fuse in one leg of the disconnect, a loose lug in a panel, a contactor pole that no longer closes, or a supply problem affecting the whole building. Which is why phase voltages and running amps on all three legs are measured before any three-phase motor is condemned, and why a compressor that failed electrically gets its supply proved before a new one goes in.
Phase loss
One leg gone. A motor already turning carries on and overheats, while a stopped one hums and stalls. On a three-phase supply the fuse that opened is often the only visible sign of it.
Voltage imbalance
Legs at different voltages. The current imbalance is far larger than the voltage imbalance that caused it, and every bit of that extra current lands in the windings as heat.
Phase reversal
Two legs swapped after work on a panel or a service upgrade. A scroll compressor runs backwards, gets loud and pumps nothing.
Commercial air handling equipment being set beside a building. Most repair work happens on the roof or in a mechanical room, above and behind the space you trade in.
What happens when we get there
Repairs on retail, restaurant and medical sites are regularly scheduled before opening or after close. Emergency work runs outside that, around the clock and every day of the year.
Trucks are stocked with the parts that fail most often on the major commercial brands: contactors, capacitors, fan and blower motors, belts, igniters, flame sensors, pressure switches, thermostats and controls. When the fault is one of those, it is repaired on the same visit. When a sealed-system component or a model-specific part has to be ordered, you get the lead time at the visit along with whether the unit can be run in a limited way in the meantime.
You hear the fault, the repair and the price before the work starts, and the invoice matches what was agreed on the roof. Our technicians are factory qualified across the major HVAC and refrigeration brands, and the company is licensed and insured.
Repair or replace, and what actually decides it
What decides it is the cost of this repair set against the remaining service life you are buying, and whether the building can carry a replacement without a second project attached to it. Age on its own is not the test.
Repair usually wins
The failure sits outside the sealed system: a motor, a belt, a contactor, a capacitor, an igniter, an actuator, a control. The cabinet, coils and heat exchanger are sound. The unit has held its charge and any leak is accessible. This is the first significant failure rather than the third in two years, and the equipment still runs on a refrigerant that is straightforward to buy.
Replacement usually wins
The compressor has failed and the rest of the machine has lived the same life. The heat exchanger is cracked. The charge has been lost more than once from a coil that cannot be repaired in place. The unit runs on a refrigerant that is now expensive and scarce. Or the load on the space changed years ago and the equipment has been running flat out ever since.
Two things specific to commercial work sit alongside that. On a rooftop change-out the existing curb usually carries the new unit through an adapter, and where it cannot, the job gains a roofing scope and a different number. The electrical service matters too, because a replacement drawing more than the old one needs a panel that can feed it. When replacement is the honest answer, you get an installed, permitted and inspected figure for the new equipment alongside the repair figure, and a straight read on how much life the repair actually buys.
What EPA 608 means for your equipment
Anyone who opens a refrigeration circuit on your premises is required to hold EPA Section 608 certification. It is a federal requirement under the Clean Air Act rather than a trade badge, and it governs how refrigerant is recovered, handled, and how systems are evacuated and charged. Our technicians hold it. In practice it means the refrigerant in your rooftop unit is recovered into a cylinder rather than released to the roof, and the equipment used to do it is certified for the job.
It also changes what counts as a repair. Topping up a system without finding the leak buys a few weeks and then loses the charge again, which is why the leak search is part of the repair. A lot of the commercial equipment still working on Long Island was built for R-22, and production and import of R-22 in the United States ended in 2020, so what remains is reclaimed and priced accordingly. On a small system with a slow seep, topping up can still be the right call. On a unit that has dropped a full charge twice in a year, it is not, and we will say so.
What Long Island asks of a rooftop, and what stops the same failure returning
Equipment on a flat membrane roof works in an environment nothing else in the building experiences, and where a unit sits on that roof changes what fails and how often. That siting question belongs to rooftop unit repair, which covers clearances, discharge air and what a roof does to a cabinet in detail.
Salt air reaches a long way inland here, and the coil is not the only casualty. Disconnect lugs corrode, contactor contacts pit faster, cabinet fasteners seize and panel screws round out, so the same fault costs more labor to reach on a coastal site than an inland one. Spring adds a cottonwood and pollen load that blocks a condenser far faster than any service manual assumes.
The building stock does the rest. A lot of Suffolk County retail and office space has been subdivided and re-tenanted several times, and the mechanical service went along with it: curbs adapted more than once, returns that suited an open floor and do not suit four tenancies, low-voltage wiring added over several fit-outs, and panels carrying load that was never recalculated.
What we change so the fault does not come back
- Amp draws logged on all three legs, visit after visit, so a trend shows before it becomes a failure
- Disconnect terminations and contactor contacts inspected and torqued, which is where a coastal site gives out first
- The gas heat sequence run end to end before the first cold night, not during it
Coils, belts, dampers and drains are on the same visit. The full scope of a scheduled service sits on the maintenance page.
Commercial HVAC repair questions we get asked most
What do you need from us when we call?
Where the equipment is and how it is reached, what it is doing or not doing, and whether anything has tripped or been reset. A photograph of the data plate is worth more than a description: brand, model and refrigerant on it decide what gets loaded on the truck before it leaves.
The unit runs but the space stays warm. Is the compressor gone?
Usually not. A compressor that has failed outright normally leaves you with no cooling at all rather than poor cooling. A unit that runs and holds warm points first at the condenser, at airflow across the evaporator, or at the charge. Condemning a compressor without pressures, superheat, subcooling and amp readings is how an owner pays for a part that was never the fault.
How quickly can somebody get here?
Emergency calls are answered 24 hours a day, every day of the year, and the typical on-site arrival across Suffolk and Nassau County is inside 90 minutes. Office hours for quotes and planned work are Monday to Friday, 8am to 5pm.
Do we have to close while you work on it?
Almost never. Rooftop and mechanical room work happens above and behind the space rather than in it, and where a repair does mean shutting down air to an area, it gets scheduled before opening, after close, or on your quietest day. Tell us your trading hours when you call and the visit is planned around them.
Tell us what the building is doing
Give us the equipment, the symptom and the address and you will get a straight answer about what it most likely is before anyone is dispatched. Serving Long Island businesses since 1999, with more than 6,000 completed commercial and residential projects behind us.
- 24/7 emergency service
- EPA 608 certified
- Licensed and insured
- Restaurants, retail, medical and office