A real rooftop unit PM visit works through seven areas: electrical, airflow, the refrigerant circuit, gas heat, the economizer, controls, and condensate. Each area has specific tasks and a reading that gets written down against the unit ID. A visit that only swaps filters and wipes a coil skips most of that, and the skipped items are the ones that cause emergency calls.
- A PM visit is judged by the readings it records, not by the time spent on the roof. No readings means no evidence the work was done.
- Seven areas need attention on every rooftop unit: electrical, airflow, refrigerant circuit, gas heat, economizer, controls, and condensate.
- Electrical and refrigerant readings only mean something when compared with the unit's own earlier readings, which is why they are logged per unit.
- The economizer and the condensate drain are the two items rushed visits skip most often, and both fail without any tenant complaint.
- Ask for the checklist itself, attached to your agreement, not just a promise of a seasonal tune-up.
How a full visit is sequenced
Order matters on a rooftop. Power is isolated and tested before anyone touches a panel, the unit is observed running before it is opened up, and cleaning comes after the as-found readings, not before. If the coil is washed first, the pressures that showed it was fouled are gone and nobody knows the unit was struggling.
- Scan the unit tag and review the last visit's notes and readings.
- Observe the unit running as found: noise, vibration, cycling, and supply air feel at the registers if accessible.
- Record as-found pressures, temperatures, and amp draws.
- Lock out power, then do the electrical, airflow, and cleaning tasks.
- Restore power, run the heating and cooling sequences, and record as-left readings.
- Photograph what changed, write up findings, and sort them into done today, needs approval, and monitor.
This is the same logic described in the broader preventive maintenance program guide, applied to a single rooftop. The tag scan in the first step is the DaVinci Portal at work: the technician sees the unit's history before opening the first panel.
Electrical and airflow tasks
These two areas explain most no-cool and weak-cooling calls. Electrical wear is gradual and measurable. Airflow loss is gradual and usually invisible until the coil ices or the compressor trips.
Electrical
| Task | What the technician is looking for | What gets logged |
|---|---|---|
| Capacitor test | Microfarad value against the rating on the can; swelling or oil residue | Rated and measured values for each capacitor |
| Contactor inspection | Pitted or burned contacts, chatter, a coil that runs hot | Condition note and photo if replaced |
| Terminations | Discolored or loose lugs, heat-damaged insulation, rodent chewing | Any lug re-torqued and any wire repaired |
| Voltage | Supply voltage under load and phase balance on three-phase units | Line-to-line voltage readings |
| Motor amp draw | Compressor, condenser fans, and blower compared with nameplate | Measured amps per motor |
| Disconnect and fuses | Corrosion, loose blades, correct fuse or breaker size on the data plate | Confirmation or discrepancy |
Work on the building's electrical service, feeders, and panels belongs to a licensed electrician. A mechanical technician reads and records at the unit disconnect and reports what looks wrong upstream. If a visit finds a supply problem, the report should say who needs to address it.
Airflow
| Task | What the technician is looking for | What gets logged |
|---|---|---|
| Filters | Correct size and rating, sealed in the rack, no bypass gaps | Filter size and condition, date changed |
| Blower | Belt wear and tension, sheave alignment, bearing noise, wheel buildup | Belt size, amp draw, any alignment correction |
| Evaporator coil | Dirt film, bent fins, slime on the pan side | Before and after photos |
| Condenser coil | Debris, grease, cottonwood or leaf matting, salt scale near the coast | Before and after photos, method used |
| Condenser fans | Blade condition, motor bearings, rotation direction, guard secure | Amp draw per fan |
| Duct connections | Disconnected or torn flex at the curb, loose access panels, missing gaskets | Findings and photos |
The refrigerant circuit and gas heat
The refrigerant side is where a gauge set earns its keep, and also where a rushed visit does the most damage by guessing. Adding refrigerant because pressures look a little low, without checking airflow and the coil first, is how a unit ends up overcharged and a leak goes unfound for another year.
- Suction and discharge pressure: read with the unit stable, interpreted against outdoor temperature and indoor return conditions, not against a fixed number.
- Superheat and subcooling: the two figures that tell a technician whether the charge and the metering device are behaving. Both are calculated and written down.
- Temperature split across the evaporator: a quick cross-check that airflow and capacity are in the expected range.
- Leak indicators: oil staining at fittings, service valves, and coil return bends, with a leak search when the charge is off. Refrigerant handling follows EPA Section 608 practice, and any added refrigerant is recorded with the amount. See the refrigerant compliance guide.
- Compressor behavior: crankcase heater function where fitted, start sound, and amp draw against the earlier visit.
- Sight glass or sensor status: where the unit has one, note moisture indicators or fault codes.
Gas heat
Gas heating sections get their own tasks, and they are safety tasks first. The technician should confirm a clean, steady ignition sequence, burner flame appearance, and manifold gas pressure, and should look at the heat exchanger for cracks, rust-through, and flame rollout marks. Flue and inducer condition matter because a restricted vent changes how the burners behave. A combustion analysis is appropriate when anything looks off, and the result goes in the record. A unit that is only run on cooling in the warm months still needs its heating section checked before the cold season, which is why the fall visit exists. The seasonal calendar explains where each task lands in the year.
Economizer, controls, and condensate
These three are grouped because they share a trait: they fail quietly and are skipped most often.
| Area | Tasks on the visit | Failure if skipped |
|---|---|---|
| Economizer | Command the actuator fully open and closed, watch the damper travel, check linkage and blade seals, confirm the outdoor air and changeover sensors read sensibly, check fault codes where the unit has diagnostics | Damper stuck closed wastes cooling capacity; stuck open brings in hot or humid air and loads the space |
| Controls | Verify thermostat or building automation signals reach the unit, confirm schedule and setpoints match what the occupants think they are, test high and low pressure cutouts, freeze protection, and limit switches | Units running on a wrong schedule, or safeties that have been jumpered out and nobody knows |
| Condensate | Clear the drain line and trap, check pan slope and standing water, test the overflow switch where installed, look for algae growth | Overflow into the ceiling below; a tenant finds out before you do |
Economizer details change by unit and by year of manufacture, and compliance expectations are tied to Title 24. When a replacement or alteration triggers acceptance testing, confirm current requirements with the permit authority. For a plain-language explanation of how economizers fit into the bigger picture, the rooftop unit guide covers them in more depth, and the building controls service covers schedules, sensors, and verification.
The readings that belong in the record
A short, consistent set of readings beats a long inconsistent one. The set below is enough to compare one visit against the next and to see drift before it becomes a failure.
| Reading | Why it is logged | What a trend can reveal |
|---|---|---|
| Compressor amps | Baseline electrical load | Rising amps point to mechanical wear, low voltage, or high head pressure |
| Condenser fan amps | Motor health | Climbing draw ahead of a bearing or winding failure |
| Blower amps and belt condition | Airflow health | Dropping amps can mean a slipping belt or dirty wheel; rising amps can mean a restricted duct |
| Suction and discharge pressure | Circuit performance | Head pressure creeping up over seasons means the condenser side is losing ground |
| Superheat and subcooling | Charge and metering | Shifts between visits suggest a slow leak or a failing metering device |
| Supply and return temperature | Delivered capacity | A narrowing split at similar outdoor conditions |
| Outdoor temperature at time of reading | Context | Makes readings comparable across visits |
Because the portal ties every reading to a QR-coded unit record, you can pull up a single rooftop unit's history instead of hunting through PDFs. That is what makes a repair-or-replace conversation grounded in data rather than opinion.
What a rushed visit skips
Rushed visits are not always dishonest. They are usually the result of a contract written around a visit count instead of a task list, with a route that leaves little time on each roof. The pattern looks like this:
- Filters changed and the report says serviced, with no readings at all.
- Coils sprayed without as-found photos, so the condition before cleaning is unknown.
- Pressures taken, but no superheat or subcooling calculated.
- Capacitors replaced by habit instead of tested, or never tested.
- Economizer assumed to work because no one complained.
- Condensate line looked at but not flushed, trap not checked.
- Heat exchanger not inspected because it is a cooling-season visit.
- Findings verbal only, so nothing is on paper for budgeting.
Contractor shall perform each scheduled visit in accordance with the attached rooftop unit checklist, covering electrical, airflow, refrigerant circuit, gas heat where applicable, economizer, controls, and condensate. Contractor shall record as-found and as-left readings for each unit and provide them to Owner with photographs and written findings after each visit. Items outside the checklist are quoted separately before work proceeds.
What to check in the report you receive
After a visit, the report should let a person who was not on the roof tell what happened. Look for a unit identifier, a date and technician, readings with units of measure, photos of coils and drains, and findings divided into done, needs approval, and monitor. If a report is a single line per unit, the contract probably needs a better checklist. The same expectations appear in our page on maintenance reporting and documentation, and the fuller context for scope is in the commercial HVAC maintenance contract scope of work.
Davinci's mechanical and controls work on these visits is performed by its own UA Local 250 crew, with no subcontractors. Electrical service upstream of the unit, roofing, and structural items are outside a mechanical PM, so the scope should name who handles them.