How to stop mineral build-up on evaporator cooler pads

Updated February 21, 2017

Evaporator coolers operate most efficiently when the maximum amount of water is evaporated on the cooling pads. Mineral deposits that collect on the cooling pads cause water to be diverted around them, resulting in areas where water is not evaporated and air circulation is blocked. This results in loss of cooling potential. Stopping mineral build-up is not feasible, but reducing it significantly is possible. Regular maintenance and some modifications to the operation of the cooler will help dramatically.

Install a bleed-off valve to the recirculating water line and connect it to a drain line that is tasked to irrigate grass such as Bermuda or Salt Grass that can tolerate the high salt content of the diverted water. Purchase a bleed-off valve at the hardware store that fits the size of the water recirculating tube in the swamp cooler. The valve is clear plastic and Y shaped. The arm on one side of the Y slides over the recirculating tube from the pump, and the other arm of the Y is half the diameter of the recirculating tube. Use a utility knife to cut the recirculating tube 12 inches up from the water pump, and slide each end of the tube into the two arms of the Y. Connect a smaller diameter tube to act as a drain line to the smaller arm of the Y and divert it to the location on the ground where it will drain.

Clean the cooler at the start of and in the middle of each season. Drain the water from the reservoir by twisting the petcock at the bottom of the cooler unit to the open position. Scrub the reservoir pan with a stiff wire brush and white vinegar to remove mineral build-up. Remove all debris from the reservoir floor by flushing with water and wiping with paper towels. Paint the reservoir pan with special water cooler paint, following the manufacturer's instructions. This paint is available at hardware stores.

Continue to clean the cooler by clearing the water distribution system of sediment build-up by flushing out the water recirculating tube with a high-pressure garden hose. Replace the entire system if it is warped or irreversibly clogged. Use a crescent wrench to unscrew the bolt that attaches the water distribution assembly to the top of the cooler. Remove the assembly and immediately remove the sediment build-up by pushing a straightened coat hanger through each water tube. The sediment will dry out and set up like concrete if this process is not completed while the sediment is still wet.

Drain and clean the reservoir once a month by following the directions in step 2 to remove sediment heavy water and the accumulation of minerals in the reservoir pan. It is not necessary to paint the reservoir floor at this time.

Treat the reservoir water with chemicals that are designed to remove mineral deposits from the system. Treat the water by pouring in the amount of chemicals indicated on the label for the size of the swamp cooler being treated. The chemicals generally require about six hours of normal cooler operation to complete the treatment and will change colour to indicate that they are spent. These chemicals increase the solubility of the minerals so they do not adhere as easily to the cooler pads. These chemicals are available at hardware stores.

Change cooling pads once a month during the season or as often as needed. Remove the cooler pad holder by lifting it straight up and swinging it out from the bottom to remove it from the cooler unit. Twist open the thumbscrew on each side of the holder, remove the filter and replace it with the new one. Secure the new filter with the thumbscrews. Paper and synthetic pads can be washed with soap and water.

Do not use softened water for evaporator water coolers because the sodium used to soften the water will form deposits on the filter pads.


Always have someone on the ground or in the house with a cell phone to communicate instructions and requests for tools or materials. Purchase supplies for the next year at the end of the current season for the best prices.


Turn the cooler off at the wall switch and place tape over the switch so it can't be turned on while the work is ongoing.

Things You'll Need

  • Bleed-off valve
  • Plastic tubing
  • Utility knife
  • Stiff wire brush
  • White vinegar
  • Paper towels
  • Water cooler paint
  • Paintbrush
  • High-pressure garden hose
  • Crescent wrench
  • Straightened coat hanger
  • De-scaling chemicals
  • Cooler pads
  • Filter
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About the Author

Freelance writing since 2009, Tom Ross has over 30 years of corporate management and hands-on experience in the supermarket industry. Ross was featured on the cover of "Instore Buyer" magazine and his articles have appeared on various websites.