Zone Damper Systems
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Zone damper systems have a zone panel, usually near the air handler, where 24v goes in and 24v goes out. The zone panel controls the dampers, which can open and close depending on where we need to send the supply air; the dampers can close when we don’t need to send air to a certain zone.
We typically encounter damper motors of two designs: spring or power-open/power-close. The latter tends to be much more common in modern zone damper systems. A control system will have common, open, and closed terminals.
A spring motor may have a wire run between common and closed; it doesn’t need to be connected to the open control because the spring will open it instead of power. When the system is not calling, the dampers will be relaxed, so they will be open.
Dampers also can’t open or close properly unless the set screw has been tightened all the way down. You can typically get an idea of how well a damper is opening or closing based on how the air resistance sounds; if the damper is working properly, the sound will change a bit.
When installing a damper motor, you need to know the orientation of your damper and make sure that the damper stops spinning when it’s supposed to stop. The size of the damper rod also matters and tends to vary by manufacturer, so you need to pay attention to get the proper repair parts.
Unlike the spring motor, a power-open/power-close motor will use common, open, and closed terminals. You can disengage the damper motor and see how freely the panel spins when you spin it yourself. If it spins freely, then you’d be able to rule out a panel jam diagnosis and could focus on the motor.
Damper systems need to be powered by a different transformer than the A/C system’s transformer, so you’ll have two transformers. The air handler may connect to common (which is a ground) and the R terminal on the thermostat, but the damper system’s terminals may connect to the actual damper system; common is NOT the same as on the A/C system. However, the staging on the damper panel needs to match the motor staging.
Many damper issues can be understood without going into the attic. You can start one zone and check to see if air is coming out of the vent. Then, turn zones on and off as necessary to see which zones are and aren’t receiving the airflow they need. Once you have an idea of the problem areas, THEN you can go into the attic.
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