Purchased an OTR microwave at discount at Lowe's. Display model, so was missing parts. Had to order damper from parts select. I had to moldify the transition part to attatch it to oven. I had to cut the opening, and bend flanges on the sides, and bore holes for screws. Then I had to create templates for attatching the unit to the cabinets and rear wall. After doing that, I turned off the electrical power, and removed the old vent hood. Removed a section of the existing vent pipe, to allow space for the transition unit and elbows. It was necessary to cut a larger opening in the bottom of the cabinet for the new vent and bore holes for the mounting screws. The old hood had a 6" round vent, and the new one is rectangular.After measuring and locating studs in the back wall, I secured the holding bracket to the wall, using long wood screws and molly bolts. I hooked the bracket into the bottom of the oven, and tilted it into place, inserting the attatching screws through the holes in the cabinet bottom into the threaded holes in the oven. After tightening the screws, checking for level, I attatched the transition unit to the vent opening above the damper. I then attached the transition unit to the existing vent pipe, installed a junction box with grounded outlet to the existing wiring. [The original unit was directly wired into the electrical circuit--the OTR unit has a plug on a power cord]. Restored power, tested unit, and all worked well.
