Commercial HVAC Maintenance Checklist

Size, quantity and the direction of airflow want recording before the old ones come out. Doing this first matters: restriction here skews every pressure and temperature reading taken afterward.

Washing from the inside out drives dirt back out the way it arrived, and whatever crowds the unit needs clearing. Of everything on the machine, head pressure tracks airflow across this coil most closely.

Dirt gathers on the upstream face, not the side within easy reach. Ice on a coil renders readings meaningless until it thaws, so pressures across ice are not worth taking.

Superheat or subcooling, matched to the metering device fitted, is the measure — pressure alone is not. Low refrigerant means a leak by definition, so a top-up without finding it is a return visit already on the books.

Oil traces give it away, since refrigerant escapes and oil stays behind. Line insulation counts as well: suction insulation that is bare or crushed loses capacity and sweats onto whatever sits below.

Dirt caked between the wheel blades drops airflow noticeably even though the motor still pulls its full current. The wheel wants to sit tight on its shaft, at the depth the housing calls for.

Only do this if the motor has an oil port or a grease fitting. Most modern motors are sealed, and adding grease damages them. If the motor does take oil, a few drops is enough. Too much grease is one of the most common ways to ruin a bearing.

The marked torque value is the target, and discoloration around contactor and terminal-block screws is the tell. Heat marks mean that joint has been arcing and it will let go again shortly, whatever it reads today.

A genuine call for heating and for cooling reveals more than the display does, and staging should follow in order. Sensor location matters too — sat over a supply register or in direct sun, it creates the very complaint behind the call.

The high-limit, low-pressure, high-pressure and rollout switches are what stop a fault becoming a fire. Test them. Do not assume they work. Never bypass one to keep a unit running: a unit that should have shut down can start a fire instead.

Deflection at the midpoint of the span should sit around half an inch, and a straightedge laid across both sheaves finds misalignment faster than the eye will. Glazed belt sides or black dust under the drive each point to slipping.

An empty trap on a negative-pressure drain draws air rather than water, flooding the pan while the line itself is technically clear. It wants refilling after flushing, and the pan has to fall toward its outlet.

A whole cycle from call to satisfied, staging and off sequence included, is what needs watching. Startup-only faults — a hard start, a contactor that pulls in late — cannot be seen on a unit already running.

Suction and discharge mean nothing next visit unless ambient and return conditions sit beside them in the record. The system also needs long enough to settle before any figure is read.

Nameplate rating is the benchmark, not merely the last visit's figure, and voltage belongs under load rather than at rest. Draw at or above nameplate is early warning of a bearing, a wheel or a supply problem.

Supply-side leaks outside the conditioned space are the costly ones, because that air has been paid for and never arrives. Wet or compressed insulation has stopped doing its job and usually signals a leak above it.

The damper wants driving through its full travel, with the linkage moving alongside the actuator instead of slipping. Stuck, an economizer either keeps the building on mechanical cooling in mild weather or floods it with unconditioned air.

Controls chasing a drifted reading run the plant hard while the space still complains. Placement deserves as much attention as the value itself, since mounting accounts for more bad numbers than outright failure.

Alarm and override history is worth reading before anything gets cleared, because a manual override left behind from an earlier call is a frequent reason a unit ignores its schedule. Setpoints and occupancy times should still reflect how the building actually gets used.

Measurements, not only actions, give the next visit a baseline to work from. What needs attention now should read differently from what can wait, with the consequence of waiting spelled out.

This box is only honest when the readings back it up, and those numbers belong in the report as the evidence. A clean result written down with real figures is what lets someone date a future fault.

Each item wants naming, with its cost and the consequence of leaving it, so a deferral is the client's choice rather than an assumption. Whatever goes undone should turn up again on the next visit's sheet.

What is unsafe needs saying in plain words, along with whether the equipment ought to stay off. When a unit is left out of service, who was told and when belongs in the record — that is the conversation people later recall differently.