Got a couple Trane pressure dependent zoning systems with RTU's that have economizers and just weighed relief dampers. Static duct pressure is controlled by a bypass duct from supply plenum to return plenum.
Problem is.......sometimes I get a slight majority for cooling, during econo enabled mode. Because most boxes are towards the closed position, the bypass is pretty open. Since the economizer is calling and most of the return duct is closed......I end up with mass amounts of supply air going into the return duct and out of the return grills.
This is the first time I have run into this.......anyone else dealt with this before?