Rooftop exhaust fan having a mechanism for locking the fan in an open position

A rooftop exhaust system for exhausting air from a building, comprising:

• a fan assembly pivotally connected to a curb or support structure and moveable back and forth from a closed position to a tilted open position;
• the fan assembly including a base, a housing, a motor disposed in the housing, and a fan driven by the motor and configured to induce air to move from the building through the fan assembly;
• a pivot arm fixed to the housing and extending therefrom and configured to pivot about an axis;
• a locking pin opening disposed on the pivot arm;
• a cam surface disposed on the pivot arm adjacent the locking pin opening;
• a plate configured to be secured to the curb or support structure;
• a spring biased locking pin mounted on the plate and aligned with the cam surface and the locking opening;
• and
• the spring biased locking pin, cam surface and locking pin opening configured such that as the fan assembly is pivoted from the closed position toward the open position, the spring biased locking pin engages the cam surface and rides along the cam surface and thereafter is biased into the locking opening which stations and locks the fan assembly in the tilted open position.