1. You may want to first test if your chiller is working by stopping your feed pump and start your chiller. If the water inside the chiller get cooled to your set value, than the chiller is ok.
2. Once the first test is done and is good, than it is most likely to be the problem of insufficient ventilation in the confined compartment that resulted with hot air being re-circulated back to the chiller. To solve this problem, a good extractor fan should be used in the compartment instead of fan blowing into it.
Just my 2 cent. Hope it help.