I've been on a quest to find the best way to cool PLA in order to get the best print quality. This is my third, and by far best, fan mount for the MendelMax 2.0 With this fan and mount, I'm getting the best print quality so far. The key was switching from the axial fan that came with the printer (and most other printers) to a blower fan like the one used on the MendelMax 2.0. See the instructions for more details.
With this single fan, I'm getting better print quality than I did before with two fans.
You can find more about my experiments with cooling fans here: http://trains.socha.com/2014/03/a-better-cooling-fan-for-pla.html
First you'll need a 24V, 50mm blower fan. I purchased mine from here:
Use two M4 x 20 screws and nuts to attach the fan to the fan mount. Then use four M3 x 12 screws to attach the air deflector to the mount. Finally, use two M3 x 10 screws and nuts to attach the fan mount to the carriage.
The wire on the fan was far too short to reach the printer board, so I cut off the connector and soldered on extension wires long enough to reach the printer board. It's best to use red and black wires as extensions so you can ensure you supply the correct power to the fan.