Evaporative Coolers

Those of you who live in humid climates will never have heard of these things, which are also commonly referred to as swamp coolers. In fact the employees at the manufacturing plants seldom have any idea why homes shipping to New Mexico or Arizona have a 14″ ceiling duct and a five way switch installed. The picture on the left is one such switch. The five positions are: off, low fan, high fan, low cool and high cool. The difference between fan and cool is that for cooling, the pump is turned on.

Think of a square box with 3″ of water in the bottom and a pump that sends the water to the top of the unit where it drips down over wood, plastic or paper batts. At the center is a large fan. When the fan pulls dry outside air through the wet batts it humidifies the air and cools it. In fact when air at 10-20% relative humidity is pulled in the temperature is lowered 25 degrees or more. For people living in dry climates it means they can have reasonably good cooling for about one fourth the cost of a compressor driven unit.

A cooler involves having a constant source of water on the roof of the home and since water leaks are common, damage can be severe. I have included a picture of the ceiling near a cooler entrance to illustrate the kind of damage that can occur if you don’t pay attention to leaks and overflows. This shows mold and mildew from water leaking in from the outside. Overflows can cause severe shingle damage (in addition to an unattractive white area on the roof). Damaged shingles will curl up and fail MUCH sooner than the rest of the roof.

These coolers are simple to maintain and repair, especially compared to air conditioning units. Their downside is that they don’t work well at all if it is humid outside. Even at their best, they can only drop the outside temperature by 20 degrees or so. In places like New Mexico, due to concerns about water usage, there have been programs developed to assist in paying for conversions from evaporative coolers to air conditioners.

and break easily. The crud that builds up in the water reservoir can jam the pumps, which promptly burn out. If the water gets too low, the pump will probably die. It is a gamble as to whether an old pump will work for a second summer or not. They are cheap, and most modern cooler boxes include an outlet letting you just unplug the old pump and plug in the new. Older coolers may force you to cut the plug off the cord and splice the wires into the electrical box on the cooler. In this case, make sure you have all the power disconnected from the cooler. Since you are likely to be making electrical repairs with wet hands while touching a metal frame, it is a good idea to be extra cautious. Fortunately, the electrical box on the cooler usually has shutoff switches as well as fuses. For the paranoid (or safety conscious), turn the switches off AND remove the fuses while working. Just think – if you do get zapped, you can look forward to falling off the roof too.

The pads play a critical role in the operation of the cooler. The different types of pads have various tradeoffs. Aspen pads have a nice smell and claim to have better cooling characteristics. They can be really messy if you have to cut them to size. The wood shreds also settle with age, so after a couple months they may develop holes at the top that will prevent the cooler from actually cooling. They also contribute more to the crud buildup in the reservoir. You definitely need the screen filter around your water pump with these pads.

Paper pads maintain their shape well even with age. If you change an old set of paper pads, it is likely that they will be crunchy and fall apart when you try to handle them. The good part is that they maintain their shape, so they keep cooling. Depending on your water hardness, they may not cool well. Once a good layer of lime builds up on the pads, the water doesn’t evaporate as well as it should so cooling will suffer. Paper pads are easy to cut to shape and will not make the mess that you can expect with wood fibers.

Plastic pads attempt to have the small air spaces of wood pads (for better cooling) while having good shape retention with age. They are also easy to cut to shape. I have had good experiences with all types of pads. If you ask around as to what people prefer, you will get a range of answers. Each has its benefits and drawbacks. Price, effectiveness and aging characteristics are the biggies.

Float adjustment can take some trial and error. Too high and water leaks onto your roof. Too low and the pads may not get enough water to cool properly (and the pump might not live as long as it should). Overflows are the bigger problem. The sneakiest cause of overflows is what happens when you turn the cooler off. You can have what seems to be the proper level of water in the reservoir, yet the cooler leaks. This can happen because when the pump pulls water during operation, the float will refill the reservoir to compensate. When the pump is turned off, much of the water drains back into the reservoir, causing it to overflow. Sometimes it seems nearly impossible to get the float adjusted properly. A good tip is to try to have the float sit as flat as possible on the water surface. This will maximize the force to the shutoff valve, so helping it do its job.

Aside from that, the squirrel cage fan needs it bearings oiled. There are typically oiling points that are easy to see when looking in the cooler. The belt eventually wears out. Eventually the fan motor will fail. When re-inserting the panels, make sure that the water tubes are correctly placed above the pads. If you turn on the water pump and hear the sound of running water dropping from the top of the cooler back into the reservoir, you need to fix it or the cooler won’t work as well. Don’t forget to install the drain stop before turning the water on. Expect to be replacing some of the water supply line (and use care to avoid crimping it forcing you to replace even more of it). Have someone downstairs to flip switches while you are on the roof, or get ready to go up and down the ladder a few times to get it all worked out.

{ 4 comments… read them below }
Joy Cintron
I have a swamp cooler the is cooling only one side of the house. I have a switch for the left side of the house and right but only one side work? how do I fix it?
Hi Joy,
I don’t understand what you mean by a switch to cool one side or the other. Is there some kind of powered baffle that moves when it is switch on or off?
The usual arrangement is for all the chilled air to be blown into the floor ducts and be distributed around the house. The amount of cooling would be controlled by opening or closing the floor registers.

della woelkers
Hey Paul, I have a 1968 falcon mobile home. In each of the rooms(except bath) there is a register in the ceiling. I believe these were put in at the factory so that the home came prepared for a roof top evap cooler. There was never one installed. The heat and a/c comes through the floor vents. When the a/c was installed they used the registers as return air, which was not efficient because the cool air was not in a duct the whole ceiling acted as on big return air duct. (not to mention that the whirl y birds let the air and tryed to cool Mesa Az. I have had the return air rerouted and seal off the hole in the ceiling. I want to blow extra insulation in the ceiling. I can access each room by the vent that are there. Do you see any reason why that would not work and the believe i am right in thinking that the mobile was built equipped for a evap
thanks, Della
Hi Delia,
Another clue would be to see if there is a five way switch in the hallway. High fan, Low fan, Pump on.
When I was working at the factory in Texas I learned the installers had no idea why they were putting those switches into homes that were going to be shipped to New Mexico
My only concern with blowing more insulation into the ceiling would be if there are “can Lights” or bathroom heat lamps that might get to hot if well insulated.

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