A lot of Tucson houses still have a metal box on the roof that their owners call a swamp cooler, and a lot of those owners spend July wondering why June felt fine. The cooler did not “break” when the humidity arrived. It ran into the limit of the way it cools. Refrigerated air — a split system, a heat pump, or a package unit — hits a different limit, on the hottest dry afternoons, and it solves a different problem. Sabino Creek Heating & Cooling replaces coolers with refrigerated air, repairs the refrigerated systems people already have, and will tell you when a cooler is still the right machine for a shop or a casita. This page is the difference, and what a conversion actually touches in the house.
What the cooler is doing
University of Arizona Cooperative Extension describes the process in plain terms. A fan draws outdoor air through pads soaked with water. Evaporation lowers the temperature of that air, and the cooler blows it into the building. The air that enters is cooler than the air outside and wetter than the air outside. That is the whole trick. There is no refrigerant loop and no thermostat holding a precise indoor temperature the way a refrigerated system does. Comfort comes from air that is cooler than outdoors, moving across you, and then leaving the house.
It has to leave. Extension notes that unlike refrigeration, which recirculates air inside the house, a cooler blows a large volume of outdoor air in, and that air needs an exhaust path: a cracked window, a door, or a ceiling vent into a ventilated attic. Close every window “to keep the cool in” and the cooler stalls. The house gets muggy and the blower labors. People coming from refrigerated air do this in the first week and decide the cooler is weak. It is starved of an exit.
Dry heat is the cooler’s weather. Extension’s pamphlet on evaporative cooler use says the machines function well except when monsoon humidity is up, and that efficiency falls as humidity rises. It also says a typical desert home will not reach what people usually consider a comfort-range temperature on days when the humidity is high. The National Weather Service defines the monsoon season as June 15 through September 30. Not every day in that window is humid. The days that are humid are the days a cooler disappoints, and they cluster when the moisture is actually here — more often in July and August than in a dry June, when Tucson’s normal rainfall is 0.23 inches against July’s 2.21 inches.
What refrigerated air is doing instead
A refrigerated system recirculates indoor air across a cold coil, pulls heat out, and dumps that heat at the outdoor coil. It also pulls moisture out of the indoor air, which is why the house feels drier in July than it does under a cooler. It can hold a setpoint. It does not need a window cracked, and an open window is now a leak, not a requirement. The outdoor unit still has to reject heat into air that, in June, is routinely above 100°F. The 1991–2020 normals put Tucson’s average June high at 101.2°F and count 68 days a year at or above 100°F. A cooler and an air conditioner can both struggle in June. They struggle for opposite reasons: the cooler because the air is so hot that even a good wet-bulb drop may not land where you want it, the air conditioner because the outdoor coil is trying to dump heat into air that is already very hot.
If your refrigerated system runs and the house still climbs on those afternoons, that is a capacity and airflow problem, covered on AC can’t keep up. It is not evidence you should switch back to a cooler for July. July’s humidity is the cooler’s weak month.
Using both, which is harder than it sounds
Extension lists three ways people use evaporative cooling: as the only system, as an alternative you switch to, or combined with refrigeration. The appeal of switching is obvious. Run the cooler in the dry weeks. Run the air conditioner when the dew point comes up. The pamphlet is blunt about the drawbacks of sharing ducts. Refrigeration ducts are often too small for the air volume a cooler needs, so the shared runs get noisy and the airflow is poor. Dampers have to separate the two machines completely. Without them, refrigerated air escapes outdoors through the cooler, and moist cooler air enters the refrigeration equipment and corrodes it. Automatic dampers exist and they need a look every year, because a damper stuck halfway does both kinds of damage slowly.
There is a second warning that people ignore because it feels efficient. Do not use the cooler to precool air that the air conditioner then refrigerates. The air conditioner has to remove the moisture the cooler just added, the indoor coil runs wetter, and the electrical use goes up. If you switch to the air conditioner for the humid stretch, drain the cooler if it will sit for several days. Extension flags standing water in the pan as a place bacteria grow, and the practical instruction is to drain it rather than leave a stagnant reservoir on the roof until September.
Pads, the pump, and the float are homeowner-maintainable on a cooler that is safely reachable. Roof units are the ones that injure people. If the cooler is on a roof, do not make a July ladder trip the maintenance plan. Mineral scale from hard water builds on pads and in the pan; Extension discusses bleed-off and cleaning as the maintenance argument, and it is a water-use argument as much as a cooling one. We are not going to quote 1990s water or electric bills as if they were this summer’s rates. The durable facts are the ones above: the cooler uses on-site water, refrigerated air uses more electricity and almost no on-site water, and which one you want depends on humidity, the house, and what you are willing to maintain. A salesman who promises a single percentage savings without seeing the house is guessing.
What a conversion actually includes
Taking the cooler off and putting an air conditioner in is not a condenser on the old curb. The house has to stop being an exhaust path. Windows get closed and weatherstripped. Ceiling vents that dumped into the attic get closed so they are not a hole. The roof opening or the side opening has to be framed and dried in, or rebuilt for whatever equipment is going there. A split system needs an air handler or a coil on a furnace, a line set, a condensate drain, a disconnect, and a circuit that matches the new equipment. Many cooler houses have electrical service and ductwork that were never asked to run a compressor. Those are part of the price, which is why we will not give you a conversion number over the phone. The factors that move a replacement price, once you are in refrigerated equipment, are on the replacement cost page.
Ducts are the part people hope to reuse and sometimes cannot. Cooler ducts were sized for a lot of air at a mild temperature drop. Refrigerated ducts want a different airflow, and leaks that were merely wasteful on a cooler become attic heat gains on an air conditioner. If the ducts are crushed, full of dust, or sized for a different machine, replacing the box and ignoring them is how a new system disappoints in its first June. Read ducts and attic heat before you accept “we’ll tie onto what’s there” with no look in the attic. Sizing still starts from the house, not from the cooler’s CFM badge. That method is what size AC a Tucson home needs.
Older single-story houses, including a lot of Green Valley homes that already use package units, convert differently from a midtown bungalow with a roof cooler and no air handler closet. A package unit on a ground pad avoids a roof curb. It still needs ducts that can carry refrigerated air, a drain, and clearance. Tell us which building you have.
When a cooler should stay, and when a mini-split is the smaller project
A workshop, a patio cover you only use in the dry months, or a casita you occupy in spring and fall can be a reasonable place to keep evaporative cooling. You accept the humid weeks, you maintain the pads, and you do not expect July to feel like the main house. A casita you sleep in through summer is a poor candidate. So is a house where someone is home all day and humidity is the complaint every monsoon. For one space that was never ducted well — a guest house, a garage conversion, an addition — a ductless system is often a smaller project than rebuilding the whole house around a central air conditioner. The limits of that approach are on mini-splits for casitas and additions.
If the main house is already refrigerated and only the casita is on a cooler, do not extend the main ducts across the yard to “save” a mini-split. You will steal air from the original rooms and dump cooling into a hot attic run. We would rather see both buildings than inherit that flex duct.
Where the DIY ends
Changing pads, checking a float, and confirming windows are cracked the right amount are homeowner work on a cooler you can reach without a roof climb. Confirming that a damper actually seals, sizing refrigerated equipment, closing a roof opening, and tying in electrical service are not. Do not run both machines with the damper in the middle “to see.” Do not vent a cooler into the return of an air conditioner. If you smell scorched insulation at a new air handler, shut it off. If you are standing on a roof in July with a panel off, come down and send the form instead.
Use the form on this page. Include the ZIP, whether the cooler is on the roof, the wall, or the ground, and whether any refrigerated equipment is already in the house. Say if the goal is whole-house refrigerated air, a casita only, or a repair of a cooler you intend to keep. We follow up the same business day. Coverage is confirmed from the ZIP; the map is on service areas. Installation scope lives under AC installation. A cooler that still cools in June and fails only on humid days is not a broken pump until the pads, the water, and the exhaust path have been ruled out. Tell us which of those you have already checked.
Sources for the figures on this page
- University of Arizona Cooperative Extension, “Evaporative Cooler Water Use,” publication AZ9145 (revised May 1994): how a cooler works, exhaust air, monsoon humidity and comfort, shared ducts, dampers, and why not to precool into a refrigerated coil. repository.arizona.edu AZ9145. Operating-cost and water-use figures in that 1994 pamphlet are not quoted here.
- National Weather Service Tucson normals and the monsoon-season definition: monthly normals and monsoon safety.
Roof access and electrical work belong to people equipped for them. This page is a decision guide, not a conversion procedure.