What do I check when a branch reads zero CFM but dampers are open?

Zero CFM with open dampers usually means a real blockage, closed/tripped device, wrong connection, or disconnected path. Trace the branch before blaming the balancer.

['If the unit is running and dampers are open but a branch reads zero, something is stopping the air. It may be internal packing/shipping material, a closed fire/smoke damper, blocked VAV inlet, crushed flex, disconnected duct, wrong tap, or a damper blade not actually moving.', 'The field move is to trace the air path from main to outlet and inspect at each choke point. Use existing access, registers, camera/mirror, pressure/noise clues, and photos. Cut access only with approval and patch it correctly.']

Airflow, Noise, Vibration & TAB 3rd Year YELLOW

Stop if

Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

Check

A hidden blockage can leave an entire zone dead and waste hours if everyone argues instead of tracing the duct path.

Steps

Confirm the balancer reading and which exact branch/zone is zero.
Check that the unit is running and main/zone dampers are actually open, not just handles turned.
Trace from main tap to VAV/damper/flex/diffuser for disconnection, crushed duct, tripped damper, or blockage.
Use camera/mirror/register access before cutting holes.
Document what you found and coordinate correction with TAB/foreman.