How To Adjust An A/C Damper

A central air conditioning system distributes the cooled air throughout your house via ducts, but how much air each room gets depends on the A/C damper settings. You're probably familiar with opening and closing the registers, but A/C dampers are plates that are located inside the HVAC system ducts, and they're adjustable.

You can open or close them as much as needed to make the rooms they control comfortable, which is handy since different rooms in your home need different amounts of cooled air. Adjusting the dampers helps redirect the air to other parts of the house that need more.

1. Open Air Conditioning Vents Fully

Open all the air conditioning vents or registers in the house so they are wide open. Turn your fan setting to the on position if your HVAC system has one. If not, change the thermostat setting to keep the system running while you adjust the dampers.

2. Find the Damper Levers

Find the air conditioning duct trunks that lead out from the furnace. Locate the damper lever on each duct. Each metal lever is located on the side of the duct. Not all HVAC systems have dampers, so look for the levers within a few feet of the furnace itself to see if you have them.

3. Open the Dampers

Open each damper by moving its lever so it points in the direction the duct travels, not across it. With all the balancing dampers open, the air conditioning air flow isn't restricted. It's operating at full capacity.

4. Close Certain A/C Dampers

Close any balancing dampers that lead to rooms that are sufficiently cooled by the air conditioning to redirect the air to other rooms. You can follow the ducts from the furnace to figure out where they go. This can help save money on air conditioning by helping the system cool more efficiently where you need it.

Turn the metal levers so they point across the ducts, perpendicular to the path the ducts follow. You may want to close the dampers on ducts that lead to small or unused rooms in the house as well. They don't require much cooling and will still receive a small amount of cooled air because the dampers don't shut completely tight.

5. Check on Room Temperatures

Wait a few days and make mental notes of the temperatures of each room in your house. Use an indoor thermometer that you move to different rooms to get an exact temperature reading. Check to determine which rooms are comfortable, which are too warm and which are too cold.

6. Make Damper Adjustments

Return to the air conditioning dampers in the furnace ducts. Adjust each air conditioning damper so it provides the right amount of air to each room. Open the dampers in ducts that lead to rooms that are too warm. Close dampers a bit to rooms that are too cool. Make small adjustments; don't open or close any damper completely.

7. Check Room Temperatures Again

Wait a few more days and repeat the damper adjustments. You need to keep doing this until the components of your HVAC system work together to ensure every room in your house is cooled to your comfort level. When you're done balancing the air conditioning dampers, use a permanent marker to draw a line on each furnace duct. Extend each line out from the handles so you know where the position should be. Make an "S" beside each line to indicate it's the summer setting.