Weak Airflow From Vents

Weak airflow means the system is producing cool air but it's not getting to your rooms with enough volume. Almost always a restriction somewhere between the return grille and the supply registers. Here's the checklist we run, in order.

Most Likely Causes

1. Dirty air filter

Always check first. A filter that's 60% loaded with dust can drop airflow by 20–30%.

2. Closed dampers

Many homes have manual dampers in the supply ductwork (small handles on the round duct in the attic). Someone may have closed them seasonally and forgotten.

3. Crushed flex duct in attic

Flex duct is fragile. A single duct that someone stepped on while replacing insulation can reduce supply to a whole room.

4. Disconnected duct in attic

Common — a duct popped off the supply plenum and is dumping all your cool air into the attic. Easy to spot during an inspection.

5. Dirty evaporator coil

A coil that hasn't been cleaned in years has dust and biofilm coating the fins, restricting airflow at the source.

6. Blower wheel loaded with dust

The squirrel-cage blower wheel can accumulate enough dust on its fins to lose 40% of its air-moving capacity. Often missed because no one ever pulls the blower for inspection.

7. Failing blower motor

Worn bearings or a weak capacitor make the blower run slow. You'll hear it (slower-than-normal start, weaker hum) before you see it.

Try These Steps Before You Call

• Replace the filter — and verify the new one is the right size and direction (arrow points toward the air handler).
• Walk the attic if accessible — look for any obviously crushed or disconnected ducts.
• Open every supply register fully.
• Check the room with the worst airflow — is the return grille in that room blocked by furniture?

Other Common AC Problems