Rooftop unit maintenance checklist for PM visits
This is a checklist for a preventative maintenance (PM) visit on a commercial rooftop unit (RTU). It covers what to check, in roughly the order a tech would do it, and a few rules of thumb that don't hold up. There's a short printable version at the end.
It's about what to check on a visit. How often each task is due is in our commercial HVAC maintenance schedule. For the wider picture, including who does the work, see our guide to commercial HVAC maintenance.
The checklist is based on ASHRAE/ACCA Standard 180, NREL's 2025 rooftop unit maintenance guide and Trane's service manuals. The manufacturer's instructions for the unit come first. NREL says the same.
What should a tech do before touching the unit?
Talk to the people in the building. Recurring complaints, like one area that's always warm, show where to look.
Then pull the fault history from the unit controller before cutting the power. Some controllers lose it when main power is turned off. Trane's manual for its Precedent rooftop units says this about its RTRM controller.
How should filters be checked?
Check the filters every visit. Clean or replace them when they're loaded.
Also check the filter fits the rack and the rack seals. If air can go around the filter, the dirt ends up on the evaporator coil instead. The DOE's Federal Energy Management Program (FEMP) guide makes this point, and Standard 180 lists filter fit and housing seal as a check.
How tight should the belts be?
On belt-drive blowers, check tension, wear and pulley alignment, and replace belts that are worn or cracked.
Set the tension to the manufacturer's spec. A fixed amount of deflection, like the often-quoted inch, isn't a reliable test. As HVAC School points out, deflection depends on the belt's length, its material and how hard you press on it. Trane, for instance, gives deflection as the belt span divided by 64, measured at a set force from a table in the manual. Trane also says to recheck new belts at least twice in the first two to three days.
What does coil and drain maintenance involve?
Inspect the condenser coil and clean it when it's dirty. Standard 180 lists it as a yearly task, and Trane says at least once a year. Units near dust, trees or kitchen exhaust need it more often. HVAC School notes that thick multi-row coils may need splitting apart to clean properly.
Check the evaporator coil for dirt and damage. Then check that the drain pan, drain line and trap drain freely and there's no standing water. Trane also lists checking that the float on the condensate overflow switch moves freely.
A dirty condenser coil and low refrigerant charge can both make a unit trip its pressure switches and restart, over and over. Our post on rooftop unit short cycling covers that in more detail.
What electrical checks belong on a PM visit?
Open the control box and look for loose or burnt terminals. Tighten them.
Check the contactors for pitting or burning. A York commercial manager writing in ACHR News made the point that replacing a contactor is much cheaper than replacing a compressor.
Measure motor and compressor amps and write them down. Don't judge a compressor by its nameplate RLA. RLA is a rating used for sizing wire and overload protection, not the current the compressor should draw. Compare running amps with the manufacturer's performance data at the current conditions. On fan motors, amps above the nameplate FLA are a fair warning sign.
Where the unit has capacitors, test them too.
How should a tech check the refrigerant circuit?
Look for oily spots on the refrigerant lines and joints. Oil leaves the circuit with the refrigerant, so an oily spot, often with dirt stuck to it, can mean a leak. NREL lists this as a yearly check.
Check that the circuit is working, using temperatures, pressures or both. Standard 180 allows either. Some trainers, including HVAC School, advise against hooking up gauges on every visit, because each connection is a chance for a leak or contamination at the service port. Many techs take a gauge reading once as a baseline, then check by temperatures and only connect gauges when the readings look off. Trane's manual does ask for suction and discharge pressures and superheat to be recorded, so follow the manufacturer for the unit you're on.
Superheat and subcooling targets depend on the metering device and the manufacturer's charts, so there's no general number to give here.
Is there a right temperature drop across the coil?
No single one. The temperature drop across the evaporator coil is a good quick check, but not a pass or fail test. Rules of thumb run from about 15 to 22°F depending on who you ask. The right number depends on airflow and indoor humidity, so compare against the manufacturer's data and against the last reading on the same unit.
How do you check the economizer?
Run the outdoor air damper through its full stroke and check the linkage moves freely. Then check the sensors and the controller are set and working. Standard 180 lists the economizer checks twice a year.
Economizers are often found not working. In one UC Davis field study, only 8 of 22 rooftop units with economizers had a working one on inspection, and 6 of those 8 were set up wrong. That's one study, not a national figure, but FEMP also notes that economizer dampers often get missed in standard maintenance.
Which safety and heating checks come before winter?
Check the thermostat and controls, and test the safeties: high limits, high and low pressure switches, and interlocks. Std 180 and NREL both list controls and safeties twice a year.
Before heating season, inspect the gas heat: burners, heat exchanger, flue and venting, and ignition. Standard 180 also calls for testing and adjusting combustion once a year. NREL adds a quarterly look at the burner for cracks, soot or discoloration.
On a heat pump, check heating mode, defrost and backup heat, and the lockout and restart setpoints. Check the outdoor coil drains and doesn't ice up. NREL notes that heat pump compressors run more hours than cooling-only units, so the compressor checks count for more. Our maintenance schedule covers the fall visit in more detail.
What else is on a full PM checklist?
A few items that the sources list and that are easy to skip:
- Fans and bearings. Check fan motors and bearings, clean the blower wheel, and grease bearings only where they take grease. Many motors are sealed.
- Cabinet and curb. Check access panels, gaskets and the curb so water and air can't get in. Replace missing panel screws.
- Duct connections at the unit, for leaks and gaps.
- Outdoor air intake screens, cleaned where fitted.
- Low-ambient head pressure control, VFDs and UV lamps, where fitted.
What should the tech leave behind?
Readings and a written report. NREL recommends keeping a detailed maintenance log, and Trane's manual includes a sample one. Amps, temperatures and pressures from this visit give the next tech something to compare against.
The report lets someone on your side decide which findings need a follow-up repair. If you use a contractor, it's worth writing this into the agreement. Our post on commercial HVAC preventative maintenance contracts covers what a contract usually includes.
Printable rooftop unit checklist
- Fault history. Read it before you cut the power.
- Filters. Replace if loaded. Check the rack seals.
- Belts. Tension, wear and alignment, to the manufacturer's spec.
- Coils and drain. Clean the condenser coil at least yearly. Drain pan and trap clear.
- Electrical. Tighten terminals, check contactors, amps against manufacturer data.
- Refrigerant. Look for oily spots. Check by temperatures, gauges if readings look off.
- Economizer. Damper through its full stroke, sensors working.
- Safeties and heat. Limits and pressure switches. Gas heat or heat pump defrost before winter.
What does a PM visit miss?
A PM visit checks each unit on one day. A 2004 PNNL paper on rooftop units found that faults like low charge or a stuck damper usually don't make anyone uncomfortable, so they "are not generally reported nor are they corrected".
SmartHVAC monitors rooftop units, split systems and commercial heat pumps between visits, around the clock. When a unit starts running differently, your team sees it and decides whether it needs a work order, can wait for the next PM visit, or needs nothing. If you'd like to see how it works on your units, book a demo.
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