The prevailing logic is that the cooler it is inside your computer, the better it will run, and a cooler system also lessens the chance of overheating and damaging components. While there are no guaranteed means of keeping your Mac cool, one of the best things you can do is ensure that it’s as dust-free as possible, thereby allowing for a better air flow within your computer.
About a month ago, my 2006 Mac Pro had gone from one of the most reliable Macs I’ve ever had the pleasure of owning to an unreliable nightmare. If I turned the Mac on and keep it running with a steady task (such as importing and converting video), and it was fine. But if I put my Mac Pro in a situation where it could fall asleep or go into any kind of power-saving mode, I’d be unable to wake it up by typing on the keyboard or moving the mouse.

After I performed a clean installation of OS X 10.7.5 and saw the same problem recur, I gritted my teeth and thought, “Look, I’ve been running this thing practically nonstop for seven years now—it may be time to retire and replace the power supply.”
One $270 eBay-purchased power supply later, I was ready to dissect my Mac Pro. Upon opening the case, the first thing I noticed was a coating of dust over everything, especially around the Mac Pro’s fans. This, combined with half a feline’s worth of hairballs scattered throughout, made me wonder about the air flowing through the machine and how the internal temperature was affected. Did my Mac Pro get to the point where the hardware and its sensors detected that it was dangerously overheating and decided to shut things down as a safety protocol? The idea began to make a bit more sense, even if it meant not tearing my Mac Pro down to its core components, installing the new power supply, and reassembling everything from there.
What followed next was about 20 minutes of pulling out the Mac Pro’s hard drives, optical drives, daughterboards, RAM chips, graphics card, and everything else I could cleanly remove and put off to the side on a safe, static-free surface. From there, I sought out every nook and cranny inside the case with a full can of compressed air, gently vacuumed up the dust bunnies and then began to pick up and clean each component with the can of compressed air.
Since reassembling the Mac Pro, the computer has run better than ever, is no louder than it was in years past, and can go to sleep and be awakened as well as when it was brand-new.

Tools for the job
If you’re looking to clean out your own Mac to help reduce its operating temperatures, Bjango’s $16 iStat Menus is an excellent application to start with and it allows you to monitor just about every operating aspect of your Mac, including internal temperature readings.
Once you feel ready to open your Mac, iFixit has a useful collection of guides for just about every Mac ever made, so visit the Web site, print out the guide that’s appropriate to your Mac, and carefully open your Mac at your own pace.
Walk into a Staples or an Office Depot, and you’re in for some degree of sticker shock at the price of compressed air, which ranged upwards of $6 per can as of my last visit. While this isn’t all the money in the world, Newegg sells compressed air for as little as roughly $4 per can. Buying in bulk saves you money, and compressed air continues to be the greatest stuff on Earth.

While compressed air isn’t naturally dangerous, it’s different from most other tools you’ll use to repair your Mac. Stick to the following tips, and you should be fine.
Don’t get too close to the computer components with your compressed air can. You’ll wind up just blowing out a dusty mess that will resettle elsewhere. Instead, aim from about four to six inches from the surface to keep the dust manageable as you blow it out of your computer.
Keep your compressed air blasts short and intermittent. The can becomes colder the longer you hold the trigger down. Be careful—the can will become so cold that it’s uncomfortable to hold. Take breaks and let the can warm up again as needed.
Avoid spraying exposed skin with the compressed air. The compressed air becomes increasingly colder and could lead to cold burns.
If you’re cleaning your Mac’s display with a can of compressed air, remember that the air won’t do the entire job. Spray the air in even motions over the display and then wipe away any excess dirt or dust with a soft, clean cloth.
Take care of your Mac and it will take care of you, even if that means occasionally opening your computer and literally cleaning it out every year or so. For the most part, opening your Mac and cleaning out the components won’t violate your AppleCare warranty, although you might want to check first or call Apple at 800-SOS-APPLE (800-767-2775) if you have any questions or concerns before opening up your Mac.
Beyond that, good luck, and if anyone’s looking for a power supply for a first-generation Mac Pro, I happen to have one on hand that I wound up not needing after all.