If the A/C is on I think the fans should run. You could have a defective fan or relay. If they are not turning they can actually deter air flow. I would test the fan with a couple jumper leads or remove the fan relay and jump the 30 to the 87A terminal in the relay socket. This should force the fan on. As Latech said your radiator may be partially plugged as well.
I would test the function of the fan first and go from there.
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