A good way of cooling the Antminer S3s is to take off the cowl and connect fans to the heatsinks. I have bought some old CPU LGA 775 fans for a less than £2 each and wedged them over the heatsinks (the clip fits between the heatsink and the metal case by the fan). You can fit 2 per side and then use a 5 way pwm splitter to power all the fans from the existing S3 pwm connector.