A couple things you'll want to check:
1. Ensure the screen filter and radiator are completely clean of dirt and debris - if no air flow is able to pass through the unit, it cannot cool.
2. If the filter and radiator are clean, place your hand over the air blowing out. If the air is hot, the unit is operating fine. If the air is cool, chances are you simply need to have your chiller recharged.
If your chiller needs recharging, simply contact a local refrigeration technician and they can recharge it for you.