Students at Rancho Bernardo High School and Bernardo Heights Middle School in the Poway Unified School District have been back in session for two weeks, but their school days have recently been shortened.

That’s because the schools’ outdated heating, ventilating and air conditioning (HVAC) system hasn't been producing consistent air conditioning and the classrooms have been heating up.

“I just know that everyone was complaining, fanning themselves off with flashcards and finding a way to step out of class and get some air,” said Mark Sladack, a student at Rancho Bernardo High.

Over the last week, he’s noticed some improvements with the air conditioning.

“I know all of last week and the week before (teachers) were starting to take the class outside, trying to get a breeze going because the rooms were just like a humid sauna,” the 17-year-old senior said.

At first, the district brought in fans. Then they ordered portable air conditioning units to bring temporary relief, according to Poway USD director of facilities, maintenance and operations Ruben Arras.

“Our plant produces enough ice to adequately supply air for both sites — both high school and middle school. And we will have air today,” he said on Thursday.

It would cost $8 to $10 million to replace the 40-year-old HVAC system.

So as a short-term fix, the district has spent about $500,000 on backup solutions and a two-month rental of a 600-ton chiller.

“We have continuous air now due to our rental chiller. We do not need to depend on the fans nor HVAC single units," Arras said. "Those were just for emergency situations. Now that we have our rental chiller, our air is flowing."

As the chiller is being installed and tested, both campuses are having students continue to only come for half-day schedules to minimize their exposure to the afternoon heat.

“I just hope that the system doesn't crash again and we have to rely on just a simple little AC unit that might not support the whole class,” Sladack said.

Arras expects all classroom air conditioning units to be fully functioning by next week, with students returning to a normal school schedule.

He said the district is exploring different proposals for long-term solutions to split and isolate the high school and the middle school HVAC systems.

All San Diego Unified schools now have air conditioning, according to an email from the district.