It's getting warm again. I live in the desert where it's much cheaper to run a swamp cooler or evaporative cooler (if you don't have laminate floors). So here's some advice.
***1. Panels: Clean the top tray. Check for rust. Take a steel brush or
sand blast them and repaint. In fact, this should be the first thing you
do, so you can let them dry while doing the other stuff. This is a good
time to also vacuum out the rest of the machine--you don't want all
sorts of dirt blowing in when you start it.
2. Check you pads. If they have to much calcification you can replace them or run some vinegar or commercially available cleaner through them. Pads should have NO AIR GAPS. I once went to my mom's place and a cheap handyman put 3 strips of the blue man-made pads in to save money. Most of the air got sucked through the gaps. If you have to do something like that because $6 is out of your budget, at least overlap the pieces. FWIW I prefer straw pads, they hold water better.
3. Maintain your pan. Clean the dirt out of your pan. If there is rust in the bottom--or even if there's not--even if you're just installing a cooler, go get some wet application roofing tar and coat the bottom of your pan. It will make the pan last 10 years or more. Cool water helps it set more quickly.
4. Lube your bearings. Check for damage to the bearings. If none, lube them a couple times. I usually lube one side, spin it, lube it again, then go to the other and lube twice in the same manner, then lube the 1st side again, then the second side again.
DO NOT used WD-40. You need a thicker oil like 30W or the stuff in the swamp cooler section with the extendable tube. I haven't had bearings go out before the cooler itself was toast, using this method.
Lube your bearings once a month.
5. Check your motor. If it doesn't grind and isn't frozen, use some electric motor/alternator/starter cleaning spray from any automotive store to clean out dust and such from your motor. In fact, if your motor turns and grinds a little, this may restore the motor for usefulness. Dirt destroys the brushes in your motor and causes it to fail prematurely.
You might want to do this again when you lube your bearings again. Considering the cost of electric motors these days, that cleaner is a good investment.
6. Replace your belt. You should be able to loosen the nut that holds it on with a 7/16" or 1/2" wrench or socket. Once you've removed the belt, check the pulleys for rust, or grit on the inside that can damage the new belt. Use a wire brush to clean them if needed. When you install the new belt, leave about 1/2" play in it. That is, the belt should not be overly tight, and the belt should move 1/2" in either direction. This extends the life of your expensive electric motor.
7. Check your pump and spider (the little tubes your water comes out of above the pads) to see if they are delivering the water evenly. If not, it's probably a small amount of straw that's gotten lodged in them. You can often blow this out using your lungs or a compressor. If that doesn't work, there's a spider cleaning tool. New spiders are cheap, and if you replace them, I don't use the MEK glue, I just push them together.
8. Assuming everything is working and clean, put it all back together and give it a test run.
Bonus tip: Increasing the pump to a larger model helps during really hot summers. Increasing the size of the pulley on the motor increases the amount of air flow, as does reducing the size of the pulley on the fan/squirrel cage. If you put a larger motor in your cooler, that will also help. Increasing all three might allow you to cool an extra 300-500 sq. ft per cooler.
10 months ago