Students at Trimmier Elementary, 4400 Success Drive, in Killeen evacuated the school due to smoke around 9:30 a.m., according to chief communication officer Terry Abbott.
Killeen firefighters responded to smoke coming through vents from the school's music room, Abbott said.
Smoke was coming from the air conditioning unit's motor, Abbott said.
"When those go out, it injects smoke into the vents," Killeen Fire Department Battalion Chief Douglas Foster said. "In the summer, you see more calls as the AC use gets more active around the city."
Killeen firefighters gave the all-clear for students to return to class around 9:50 a.m. The students were evacuated for about 20 minutes, according to Foster.