I've been working on a building that I'm incountering some high building static pressure problems. I've been told that this has been going on for about 6 years now. This is a three story building and has two McQuay RDT roof top units one controls the west side of the building all 3 floors and the other the east side all 3 floors. The building doors will hang open when the units are in Economising mode only, when mechanical cooling is on or in the heat mode this seems to not be an issue. What I have checked is all fire and smoke dampers in the building. all exhaust fans for the building are running and none are interlocked with the roof top units. Inspected return and ODA dampers and linkages. Reilief dampers on the RTU's are none mechanical and will swing freely open. I've inspected RA fan for proprer rotation. The east unit seem's to have a lower speed and less air comming from the relief damper and has had my main focus. One thing I did find on the east unit was that a new VFD has been installed for the supply fan and was not communicating with the Microtech controller. I've installed a 10VDC to 10VDC to boost the voltage signal to the RTU and now the supply fan is working properly with the roof top and can be controlled from the microtech. I guess in short im wondering if anyone had some ideas that are common with these units where im getting my excess ODA from. Any help would be great.