Help with Chiller

[Jaws]

I've got a Pacific Coast CL-650 1/4 hp chiller. It's done a great job keeping my 180G tank at the right temperature for the most part. Even on some of the really hot days it kept the temperature around 80 which was fine. Now, even that it's not that hot out lately, the chiller struggles to keep the temperature below 83. Any ideas what I'm looking at here?