Yeah, let's rule out overcharge/undercharge as earlier suggested. He never that said it wasn't getting cold. For it to be overcharged, someone would have has to have overcharged it (again not mentioned). The info given leads me to either the belt tensioner (idler pulley) as I suggested or the belt itself.
2005 Pontaic GTO - CGM 6 Speed (My car)
1983 Chevrolet El Camino Conquista (My daily driver)
2010 Mercedes Benz C300 Sedan (Wife's car)
2014 Kia Rio LX (Wife's daily driver)