The worker, 55, and his colleagues were repairing the elevator at 1209 Loring Ave., near Bishop Clarence V. Keaton Boulevard, about 10:45 a.m. on March 29 when the suspect demanded to use it, police said.
The workers told him he couldn't use it and then left the building, trying to avoid further confrontation, police said.
But the suspect, who can be seen in surveillance video police released Sunday, followed them outside and punched the 55-year-old in the back of the head, knocking him to the ground, police said.
THe victim was treated at Brookdale Hospital, police said.
The suspect, who was described as standing about 6-foot-2, fled the scene and hadn't been arrested as of Monday morning, police said.
He was last seen wearing a blue jacket, white jeans and white sneakers, police said.
Anyone with information should contact Crime Stoppers at (800) 577-TIPS (8477).