You hold your hand in front of the vent and the air is cold but barely moving. It used to blow hard enough to feel across the room. Now you have to stand directly in front of the vent to feel anything.
Weak airflow means less cooling reaches the room, even if the air temperature is correct. The system is working, but something is choking it.
Causes you can check
Dirty air filter. The most common cause of weak airflow in any AC system. A clogged filter is a wall between the return air and the blower. Replace it. If airflow improves immediately, the filter was the entire problem.
Blocked return grille. The return grille is where the system pulls air in. If it is covered by furniture, a rug, or stored items, the blower is starved for air. Clear it.
Closed dampers. Some duct systems have manual dampers — small handles on the branch ducts near the trunk line, usually in the attic or a closet. If a damper has been closed (rotated perpendicular to the duct), the room it serves gets no air. Check any accessible dampers.
Causes that need a technician
Failing blower motor. The blower motor drives the fan that moves air through the duct system. As it ages, the bearings wear and the motor slows down. A blower running at 60 percent speed moves far less air than one at full speed, but the sound difference is subtle. A technician can measure airflow at the registers and compare it to the system's rated CFM.
Bad blower capacitor. The run capacitor powers the blower motor. A weakening capacitor causes the motor to run at reduced speed. This is a common, inexpensive repair.
Collapsed or kinked flex duct. Flex duct in the attic can sag, kink at a turn, or collapse under its own weight if the supports fail. A collapsed section reduces airflow to a trickle even though everything else is working correctly. This requires getting into the attic and re-supporting or replacing the affected run.
Dirty evaporator coil. A coil caked with debris creates resistance to airflow even with a clean filter. The blower pushes air through the coil, and a dirty coil is like a second filter. Professional cleaning is required.
Leaking ductwork. If a major joint or connection has opened up, cooled air is blowing into the attic instead of into your rooms. The blower is working at full capacity, but the air never arrives. Duct inspection and sealing fixes this.
How to tell which one
If every vent in the house is weak, the problem is at the air handler — filter, blower, coil, or a major duct disconnection near the trunk line. If only one or two vents are weak, the problem is in the branch duct serving those rooms — a kink, collapse, disconnection, or closed damper.
Call (727) 477-3256 and tell us whether the problem is the whole house or specific rooms. That tells us where to look first.
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