RELIEF FROM THE oppressive heat on subway platforms is on the way. The Second Ave. subway, the No. 7 line extension and the South Ferry station will be outfitted with special air-cooling systems to reduce the temperature along platforms, the MTA revealed yesterday. Metropolitan Transportation Authority spokesman Tim O'Brien couldn't predict what the cooler temperature range would be in the stations, but he promised noticeable relief. "Days like today will feel like early October in Central Park instead of mid-summer in Hades," O'Brien said. Under the plan, hot air in the stations will be funneled through "air chillers" and then pumped onto the platforms, O'Brien said. Fans will then help distribute the cooled air. The stations also will have equipment capable of pulling in fresh air from the streets above, he said. But straphangers will have to keep sweating for a bit longer. The new South Ferry station in lower Manhattan isn't scheduled to open until 2008. The first stretch of the Second Ave. subway, running from 96th St. to the existing 63rd St./Lexington Ave. station, is slated to open in 2013, as is the No. 7 line extension to the West Side. Cooling existing stations in the vast subway system, which dates back to the early 1900s, would be difficult and costly, transit officials said. "New stations are blank slates and we can utilize the most modern technology to cool the platforms," O'Brien said. "When you are starting from scratch, there are are a lot of engineering options, as opposed to working on something that's been there for 100 years." Suffering straphangers said they're for anything that will cool off subway platforms. "It's long overdue," Teo Ortiz, 52, a retired school safety officers, said in the sweltering Times Square station. "It's miserable on the platforms."