Commercial VAV Box Not Working

Likely causes

These categories help organize the diagnostic process; they are not a remote diagnosis.

• Failed actuator, controller, sensor, flow pickup, damper, wiring, or communication
• Insufficient primary air, high or low static, duct restriction, or upstream schedule problem
• Reheat valve, electric heat, hot-water flow, discharge sensor, or sequence fault

Safe facility observations

Facility staff may record alarm text, thermostat or BAS display status, affected areas, time of onset, visible water or ice from a safe location, and unusual sound or odor. Do not open energized panels, reset a repeatedly tripping breaker, bypass safeties, force controls, handle refrigerant, work on combustion equipment, or enter pressure systems.

• Record zone temperature, setpoint, occupancy, airflow shown, damper command, and alarms
• Note whether the problem affects one zone or many
• Do not force outputs or enter ceilings without facility safety authorization

Professional diagnostic process

Diagnosis compares zone demand, sensor accuracy, airflow pickup, command, actual damper, primary air, static pressure, reheat, discharge temperature, communication, and sequence.

Equipment commonly involved

The fault can originate in the primary equipment or a connected system.

• VAV terminal
• Actuator and controller
• Zone and discharge sensors
• Reheat coil or electric heat

Risks of delay

Delay can cause persistent comfort complaints, ventilation imbalance, simultaneous heating and cooling, frozen coils, high energy use, or moisture problems.

Repair considerations

Repair the verified terminal, sensor, air, heat, wiring, network, or sequence cause and verify the zone under relevant operating modes.

Replacement considerations

Consider controller, actuator, pickup, heat, or entire terminal replacement based on access, condition, controls platform, duct, parts, and renovation plan.

Related maintenance

Review sensors, pickups, dampers, actuators, reheat, valves, airflow calibration, communication, overrides, alarms, and zone trends.

Safety notice

This guide is educational and is not a substitute for on-site diagnosis. Follow facility safety procedures and applicable code. If there is smoke, fire, suspected gas, exposed electrical damage, a significant refrigerant release, pressure hazard, or an immediate life-safety concern, evacuate or isolate the area as appropriate and contact emergency or qualified response personnel.