When you say its "clean" what does that mean? You washed it? Blew Air through it? Used a cleaning solution?  Simply blowing air or washing is not always enough. Some dirt will get caked onto the fins and they will not cool properly, there are products that will loosen this up and then you can wash that out.

Are the coolers "stacked" on those? If so you need to seperate them to truely clean them well.