Standard Operating Procedure: RTU Preventive Maintenance

This Standard Operating Procedure (SOP) outlines the mandatory preventive maintenance (PM) protocol for Rooftop Units (RTUs). The objective is to maximize equipment longevity, ensure occupant comfort, maintain energy efficiency, and prevent catastrophic failures. All technicians must adhere to these safety and procedural guidelines to remain compliant with environmental regulations and internal safety standards. Ensure all Lock-Out/Tag-Out (LOTO) procedures are strictly followed before initiating any internal component inspections.

Phase 1: Pre-Maintenance & Safety Protocols

• Verify unit status and note any existing alarms on the Building Automation System (BAS) or thermostat.
• Perform LOTO on the electrical disconnect switch.
• Don appropriate Personal Protective Equipment (PPE), including safety glasses, gloves, and ear protection.
• Clear debris from the roof area surrounding the unit to ensure adequate airflow and workspace.

Phase 2: Cabinet & Airside Components

• Remove all access panels and inspect for signs of rodent damage, nesting, or water intrusion.
• Inspect, clean, and replace air filters. Log the pressure drop across the filter bank.
• Inspect blower motor, pulley, and belt tension. Check for signs of fraying, cracking, or excessive vibration.
• Clean the evaporator coil using approved foaming cleaner; ensure the condensate pan is clear and the drain line is free-flowing.
• Verify the operation of dampers and actuators for Economizer functionality.

Phase 3: Refrigeration & Compressor System

• Inspect the condenser coils for debris, cottonwood, or dirt buildup. Clean using a low-pressure water spray (fin-safe).
• Check refrigerant lines for signs of oil stains, which indicate a potential leak.
• Measure and record compressor amperage and voltage against the data plate specifications.
• Check contactors for pitting or burnt terminals; tighten all high-voltage electrical connections.
• Test refrigerant pressures (suction and discharge) and calculate superheat and subcooling values to ensure optimal charge.

Phase 4: Heating & Electrical Controls

• For Gas-Fired Units: Inspect heat exchanger for cracks or rust, clean burners, and verify proper ignition/flame rectification.
• For Electric Heat: Test sequencer and heating elements for continuity and amp draw.
• Inspect low-voltage control wiring for loose connections.
• Verify setpoints and communication status with the BAS gateway.

Phase 5: Final Testing & Documentation

• Reinstall all access panels and verify secure seals.
• Restore power and initiate a test sequence via the controller.
• Confirm unit transitions correctly between heating, cooling, and economizer modes.
• Complete the PM log, documenting all measurements, parts replaced, and recommendations for future repairs.

Pro Tips & Pitfalls

• Pro Tip: Always clean condenser coils from the inside out if the design allows, ensuring debris is pushed out rather than further into the fins.
• Pro Tip: Use an infrared camera to quickly identify "hot spots" on electrical terminals before they lead to arcing or failure.
• Pitfall: Do not use high-pressure washers on aluminum condenser fins, as this can flatten the fins and permanently restrict airflow.
• Pitfall: Never ignore a recurring refrigerant leak; "topping off" is a temporary fix that masks underlying piping failures and environmental hazards.

Frequently Asked Questions

Q: How often should RTU maintenance be performed? A: Standard industry practice suggests a minimum of semi-annual inspections—ideally once in the spring before cooling season and once in the fall before heating season.

Q: What is the most common cause of RTU failure? A: Neglected airflow restrictions, specifically dirty filters and clogged condenser coils, which cause the compressor to overwork, leading to premature burnout.

Q: Should I clean the condensate drain with bleach? A: No, avoid harsh chemicals. Use a manufacturer-approved drain pan tablet or a mild enzymatic cleaner to prevent corrosion of metal pans and damage to surrounding components.