Light Commercial Rooftop Unit Service SOP

Purpose

Standardize service for light commercial rooftop units (RTUs) - the packaged HVAC systems on small office, retail, restaurant, + light industrial buildings. RTU service is the bridge from residential HVAC to commercial; pricing + scope are different + more profitable per labor hour.

Scope

Single-package + split RTUs from 3-25 tons. Common brands: Carrier 48HC, Trane Voyager + Precedent, Lennox LRP, York Sunline, Daikin Rebel. Excludes large commercial chillers + air-handling units (separate trade).

Prerequisites

• HVAC license valid for commercial work
• EPA 608 Universal (or Type II minimum)
• Fall protection per OSHA (roof work)
• Ladder + roof access plan
• Toolset: standard HVAC + commercial-specific (megger, amp clamp 100A+, water-column manometer)
• Refrigerant per system label (R-410A still common in fleet; R-454B + R-32 for 2025+ replacements)
• Combustion analyzer (gas-fired RTUs)
• 2-3 hours per typical annual visit

Pre-arrival

1. Confirm rooftop access (door from interior OR external ladder)
2. Coordinate with building manager / tenant
3. Note any specific complaints
4. Pull last service history if available

Procedure

Step 1: Site assessment + safety

1. Roof access PPE: fall protection per OSHA above 4 ft
2. Walk roof; identify hazards (skylights, soft spots, recent storm damage)
3. Verify unit location matches work order
4. Read unit nameplate: voltage, amps, refrigerant type, model, serial, manufacture date
5. Note physical condition: rust, hail damage, panel security

Step 2: Electrical safety

1. Lockout/tagout main disconnect for safety inspection
2. Verify with meter at terminals
3. Inspect electrical panel: connections, scorching, wire condition
4. Replace any wire nuts or terminations showing heat damage

Step 3: Filters

1. Note filter size + MERV rating
2. Replace OR clean per system
3. Most commercial RTUs use 2" 16x25 pleated filters (multiple positions); typical 4-6 filters per unit
4. Document filter change date for next service interval

Step 4: Coils

1. Outdoor (condenser) coil: visual + clean
2. Indoor (evaporator) coil: inspect from filter side; check drain pan
3. Coil cleaning if needed: foaming coil cleaner, pressure rinse from rooftop access
4. Watch coil fin damage; comb if needed

Step 5: Belt drives (older units)

1. Inspect belt for wear, cracks, glazing
2. Check tension (typical: deflect 1/2" with thumb pressure)
3. Replace if worn
4. Note belt size + model for future service

Step 6: Bearings + lubrication

1. Spin fan + blower wheels; listen for rumble or grinding
2. Lubricate bearings per manufacturer (zerk fittings if equipped)
3. Belt drive blowers usually have grease zerk; direct drive sealed

Step 7: Refrigeration check

1. Connect manifold to service valves
2. Run system 15+ minutes to stabilize
3. Record suction + discharge pressures
4. Calculate superheat (TXV systems) or subcooling (most modern)
5. Compare to manufacturer chart
6. Note any anomalies

Step 8: Combustion (gas heat)

1. Confirm gas supply pressure (typical 5-7 in WC inlet, 3-3.5 in WC at burner manifold)
2. Light burner; observe flame
3. Combustion analyzer in flue: CO2 8-9%, CO < 100 ppm, draft -0.02 to -0.10 in WC
4. Inspect heat exchanger for cracks (mirror + flashlight)
5. Verify limit + roll-out controls
6. Check vent integrity

Step 9: Economizer (if equipped)

1. Test full operating range
2. Outdoor air damper opens at acceptable outdoor conditions
3. Linkage operating freely
4. Calibrate sensors
5. Verify minimum outside-air position (ASHRAE 62.1 commercial ventilation)

Step 10: Controls + thermostat

1. Test heating + cooling stages
2. Verify fan operation
3. Test economizer integration
4. Check thermostat batteries (commercial usually 24V; some battery-backed)
5. Set commercial schedule per tenant

Step 11: Drains

1. Condensate drain clear
2. Pan tilt verified
3. Trap intact + filled
4. Overflow safety switch tested

Step 12: Document + close

1. Service report with all readings
2. Recommendations list (repairs, upgrades)
3. Customer signature
4. Photos of completed work
5. Lock back up

Acceptance criteria

• All function tests passed
• Readings within manufacturer specs
• Filters replaced/cleaned
• Combustion within spec (gas units)
• Drain functional
• No active alarms
• Customer signed work order

Common pitfalls

• No lockout/tagout: serious injury risk on commercial 3-phase
• Skipping economizer check: tenant complaint about IAQ + energy waste
• Wrong gauge type: commercial sometimes 3-phase + different connections
• Combustion not analyzed: CO levels not verified
• Drain trap dry: pulls air through pan, dries out, develops smell
• Missing the heat exchanger crack: CO into the building, life-safety
• No service report: tenant + property manager disputes work

Safety considerations

• Roof work: harness, anchor point, ladder safety
• High-voltage 3-phase: PPE, glove rating, voltmeter testing before touching
• Refrigerant under pressure: gauges + recovery
• Combustion: CO testing every time
• Tight rooftop spaces: heat exhaustion risk in summer
• Confined-space if working inside ductwork section

Differences from residential

• Higher voltages (208/230/460 3-phase common)
• Multi-stage equipment + economizer
• Tenant management coordination
• Service contracts vs one-off calls
• Commercial spec sheets + AHJ documentation
• ASHRAE 62.1 ventilation requirements
• Documentation more important for property manager records
• Multiple units per property = recurring revenue at scale

Customer talking points

For property managers:

1. "Annual contract covers $X per unit, includes [coverage list]"
2. "Identifies issues early; saves 30-50% vs reactive repair on average"
3. "Building uptime + tenant comfort"
4. "Compliance documentation for ASHRAE 62.1 + insurance"
5. "Predictable budget vs surprise major-repair calls"

Multi-unit property managers respond to ROI + uptime, not technical detail.

References

• ASHRAE 62.1 Ventilation for Acceptable Indoor Air Quality (commercial)
• ASHRAE 90.1 Energy Standard for Buildings (commercial)
• AHRI 340/360 Performance Rating (packaged equipment)
• NFPA 90A + 90B (commercial HVAC)
• Manufacturer service manuals
• Manuall internal: Annual HVAC System Maintenance, Refrigerant Leak Diagnosis Troubleshooting