iO HVAC Controls MD-12 Md Series 12 Round 3 Wire Damper Po/PciO HVAC Controls MD 12 MD Series 12 Round 3 Wire Damper PO PC The MD Series dampers are perfect for use with most zoning systems and recommended for use with our iO ESP 400 and ESP zone panels. These dampers are shipped complete and ready for installation. The MD Series dampers can be installed in any position. They are rated for duct systems less than 1. 0 WC. The MD Series damper has a simple adjustment for setting the minimum position. Features and