HVAC Airflow Damper Troubleshooting Guide

Check your dampers with this troubleshooting guide, on the MCDLG Newsstand. Make sure your HVAC system is in peak condition. 

What happens when an airflow damper fails? You may not know right away, since most dampers are installed in ducts or openings attached to ductwork.

If you have issues with airflow in your HVAC system, then the culprit might be a faulty damper. A failed damper can cause issues with other components in the HVAC system:

• Failure to close causes the HVAC system to overcompensate when heating or cooling other zones in the building, which puts extra strain on the system.
• Failure to open can damage ducts and fans as the HVAC system tries to push air through a closed-off duct, which leads to a higher repair bill.
• Modulating issues can create pressure imbalances that lead to weird drafts or hot/cold spots in rooms.
• If any of the blades do not move, then this indicates an issue with the blade’s axle or its bearings. Technicians can replace bearings in the field using manufacturer approved parts. If you determine the axle is the issue, then you will need to replace the damper.
• If the blades move freely on their own, then this indicates an issue with the damper’s linkage. Check the linkage – along the side of the damper or attached to the face of the damper’s blades – and look for signs of damage. Checking the linkage may require removing the damper from the duct. Tighten any loose connections between linkage segments and connections between linkage and blade.
• If the linkage has been detached from any of the blades, attempt to reattach them in the field using manufacturer approved parts. Otherwise, return the damper to the manufacturer for repair or replacement.

Here is a guide for troubleshooting airflow dampers.

Step 1 – Locate the Damper and Detach the Duct

Find the damper. Airflow dampers are often installed inside ductwork. On occasion, they may be installed between duct sections, inside a wall opening, or on the face of a wall opening.

If your damper is in a duct, look for these indicators to help find it:

• The actuator may be mounted to the duct exterior, to free up space inside the ductwork. Look for an actuator. 
• Installers will often mark the damper's location with a sticker or writing on the duct with a marker.
• If the damper isn't marked, look for mounting screws along the duct exterior. If the screws appear on more than one side of the duct exterior, then it's likely the damper.

Once you find the damper, detach the ductwork from the damper on one side. This will provide a direct view of the damper’s face.

Step 2 – Test Damper with the Actuator

Actuators are attached to the damper’s driving blade shaft, which extends beyond the damper’s frame. This extended shaft will drive blade rotation for all blades in the damper.

For electric actuators, find and disconnect the power supply wiring to the actuator. In certain situations, the actuator may have a test function: either a switch on the actuator for testing power, or a dedicated test box for testing the actuator.

If your actuator has a test function, then use that method to test the actuator’s function. For pneumatic actuators, remove the air supply line and replace it with a test pump.

Watch the damper’s blades when testing the actuator. All blades should rotate on the same action, cleanly and without resistance.

If the actuator has a position indicator: Make sure the actuator indicates the correct position when testing the damper. The position indication switch should show “open” when the damper is fully open.

For modulating actuators: Cycle through each modulation point using the. Ensure the damper properly holds each blade position indicated on the actuator.

Hand quadrants, hand cranks, worm gear operators, and chain-wheel operators are all manual actuators. Operate the manual actuator to perform this test.

Step 3 – Diagnose possible issues

The blades do not rotate with the actuator: Detach the actuator from the damper’s driving axle and test the blades by hand. Twist the extended axle that was attached to the actuator. All blades should rotate on the same action.

The blades rotate by hand, but not by actuator: Fasten the actuator to the driving axle and apply power to reevaluate. Ensure the fastening arm is secured to the damper’s blade axle. If the blades do not rotate after this adjustment, replace the actuator.

One or more blades do not rotate: This is known as “seizing” or “binding”, when the blade refuses to rotate. Check each immobile blade to determine whether they rotate on their own.

Only the driving blade rotates: This indicates an issue with the damper’s linkage. Check the linkage connection at the driving blade and ensure it is properly attached. If the linkage is damaged, return the damper for repair or replacement.

One or more blades rotate slowly: Apply dry graphite lubricant to the blade axle. This may alleviate issues with slow rotation. If the problem persists, replace the rotation bearings or return the damper for repair or replacement.

The modulating position is incorrect: Set the actuator to the position that needs correcting. Loosen the actuator from the driving blade shaft. Use the blade shaft to rotate the blade to the correct position, when tighten the actuator to the blade shaft.

Step 4 – Clean and Lubricate the Damper

Clean dampers perform their best. Use lint-free cloth to remove dust and grit from blade surfaces, blade axles, and other moving parts. Use light detergent solutions for the best cleaning. MCDLG recommends a 5% solution for cleaning damper components.

Apply dry-graphite lubricant to moving parts, such as the blade axles and the linkage.

Test the damper after cleaning and lubricating to ensure it opens and closes freely.

Step 5 – Reattach the Duct.

Once you have finished final testing, reattach the duct to the damper to complete the damper maintenance.

Repeat these steps for each damper. Perform regular maintenance on your dampers to quickly diagnose and address issues. A regular maintenance schedule is the best way to prevent damage to your HVAC system.