My house has a zoned HVAC system with 2 zones and a single furnace and a single AC unit. The downstairs zone is about 2200 sq ft and the upstairs zone is only 250 sq ft. There is a duct that runs from the supply side of the air handler directly back to the return side of the air handler. The duct has what appears to be a spring-open damper in it. It appears that the damper is always in the open position regardless of which zone is calling for cooling or heat since there is no power hooked up to it. I thought it might be pressure activated so I ran the fan for both zones today but regardless of which zone was controlling the fan the damper stayed open. It is my understanding that this bypass damper would only be used when the smaller zone is in operation. Should this damper be doing something?

Thanks in advance for your responses.