Why does my swamp cooler smell musty when it starts?

Stale water and old pads. Water that sat in the pan grows a film, and aspen pads hold it. Draining the pan, scrubbing it and fitting new pads at spring startup solves most of it. A working bleed-off keeps it from returning.

Can I run the cooler and the air conditioner at the same time?

No. The cooler adds moisture the air conditioner has to remove, and the open windows a cooler needs let the cold air out. Pick one for the day. The cooler owns the dry months, the AC owns the monsoon.

How often do the pads need replacing?

Aspen pads every spring, sometimes twice in a hard summer. Rigid media lasts several seasons if the bleed-off is working and the water is managed. Either way, a white mineral crust on the pad face means the water is too concentrated.

There is a white crust on the pads and the cabinet. What is it?

Mineral scale from hard Valley water. Evaporation leaves the minerals behind, and without a bleed-off or purge pump they concentrate until they coat everything. It shortens pad and pump life and is the reason the purge line matters.

Do I really need to winterize a cooler in Phoenix?

Yes, but not for the reason people think. Freezing is rare. The real damage is a wet pan rusting through the cabinet and an open duct dumping your heated air onto the roof all winter. Drain it, cover it, close the damper.

Is a cooler cheaper to run than air conditioning?

On electricity, by a wide margin, because it has no compressor. On water, it is not free. And it only delivers when the air is dry, so the comparison holds in May and falls apart in August. Our field note on the high summer electric bill puts the numbers in context.

Can a new cooler cool my whole house in July?

No. A new cooler is still an evaporative cooler, and monsoon humidity limits it the same way it limited the old one. If July comfort is the goal, the answer is refrigerated cooling. Our evaporative cooler replacement page covers both paths.

My cooler is leaking water onto the roof. Is that an emergency?

Shut the water supply off and turn the unit off. It is usually a stuck float or a cracked pan, and both are simple repairs, but water pooling around the duct curb finds its way into the ceiling quickly. Do not go up to look. Call and we will.

Why does my swamp cooler smell musty when it starts?

Stale water and old pads. Water that sat in the pan grows a film, and aspen pads hold it. Draining the pan, scrubbing it and fitting new pads at spring startup solves most of it. A working bleed-off keeps it from returning.

Can I run the cooler and the air conditioner at the same time?

No. The cooler adds moisture the air conditioner has to remove, and the open windows a cooler needs let the cold air out. Pick one for the day. The cooler owns the dry months, the AC owns the monsoon.

How often do the pads need replacing?

Aspen pads every spring, sometimes twice in a hard summer. Rigid media lasts several seasons if the bleed-off is working and the water is managed. Either way, a white mineral crust on the pad face means the water is too concentrated.

There is a white crust on the pads and the cabinet. What is it?

Mineral scale from hard Valley water. Evaporation leaves the minerals behind, and without a bleed-off or purge pump they concentrate until they coat everything. It shortens pad and pump life and is the reason the purge line matters.

Do I really need to winterize a cooler in Phoenix?

Yes, but not for the reason people think. Freezing is rare. The real damage is a wet pan rusting through the cabinet and an open duct dumping your heated air onto the roof all winter. Drain it, cover it, close the damper.

Is a cooler cheaper to run than air conditioning?

On electricity, by a wide margin, because it has no compressor. On water, it is not free. And it only delivers when the air is dry, so the comparison holds in May and falls apart in August. Our field note on the high summer electric bill puts the numbers in context.

Can a new cooler cool my whole house in July?

No. A new cooler is still an evaporative cooler, and monsoon humidity limits it the same way it limited the old one. If July comfort is the goal, the answer is refrigerated cooling. Our evaporative cooler replacement page covers both paths.

My cooler is leaking water onto the roof. Is that an emergency?

Shut the water supply off and turn the unit off. It is usually a stuck float or a cracked pan, and both are simple repairs, but water pooling around the duct curb finds its way into the ceiling quickly. Do not go up to look. Call and we will.

Evaporative Coolers in the Phoenix Desert

Evaporative Coolers in the Desert

Water, a pad, a fan and a dry sky. That is the entire machine. Here is why it works from April to June, why it gives up in July, and how to decide whether yours is worth keeping.

Cools by evaporation, not refrigeration

Loses ground as the dew point rises

Pads, pumps and floats wear every season

Keep it, combine it or replace it

Schedule today — we’re here 24/7.

Veteran Owned & Operated

How evaporation cools a house

A swamp cooler does one trick. A small pump lifts water from a pan to a trough that drips over a pad. A blower pulls hot outside air through the wet pad. Water evaporates into that air, and evaporation takes heat, so the air that comes out is cooler and wetter than the air that went in. The blower pushes it into the house, and because the house is being filled with outside air, something has to give: an open window or a relief damper. A cooler does not recirculate. It ventilates. A house on a cooler changes its entire volume of air many times an hour, which is why it smells like outside and why dust comes along for the ride.
The cooling you get depends on the gap between the air temperature and its wet-bulb temperature. When the air is bone dry, the gap is wide and a good cooler can drop the supply air twenty degrees or more. When the air is humid, the gap collapses and so does the cooler.

Why it works in May and fails in August

Phoenix in May: 100 degrees and single-digit humidity. Evaporation is fast, and a cooler is nearly unbeatable for the electricity it uses. It runs a pump and a fan motor, no compressor.
Then the monsoon arrives. The dew point climbs, and the same cooler that produced pleasant air in May now produces warm, damp air that feels like a locker room. The pads are still wet. The pump is still running. The physics simply stopped cooperating. That is not a fault, and no service call fixes it. Homeowners who inherit a cooler sometimes spend a July convinced it is broken. It is not.

The parts and what they do

Pads and media

Aspen pads are shredded wood in a mesh sleeve: inexpensive, replaced every spring, sagging and channeling by midsummer. Rigid cellulose media is a thick honeycomb block that lasts several seasons with good water management and evaporates more efficiently, at a higher upfront cost.

Pump

A small submersible pump lifts water to the distribution tubes. Valley water is hard, and mineral scale collects on the impeller until it stalls.

Float valve

A fill valve, like the one in a toilet tank, that holds the pan level. When it sticks open, the pan overflows onto the roof and into the duct curb.

Motor and blower

Most residential coolers use a belt-driven blower with a two-speed motor. Belts glaze and crack, bearings want oil, and a squeal at startup is the first warning.

Bleed-off or purge pump

A line that dumps a little water continuously, or a pump that empties the pan on a timer, so minerals do not concentrate. Without one, the pads crust white within weeks.

Where you find it in Phoenix homes

Coolers live on the roofs of flat and low-pitched homes from the 1950s through the 1970s in central Phoenix, Glendale, Mesa and Tempe, with a duct dropped through the ceiling into the hallway. Side-discharge units hang on a wall beside older ranch houses. Many of these homes now run both a cooler and a refrigerated system, each in its season. Tract homes built after the 1980s almost never had one. If yours is a pre-war house with no ducts at all, our page on historic home HVAC covers the choices.

Mixing a cooler with refrigerated AC

The two can share a house. They cannot share an hour. A cooler pushes humid air into a home the air conditioner is trying to dry, and the open windows a cooler needs let the AC's cold air walk out. Run the cooler through the dry spring, then switch to the refrigerated system when the dew point climbs. The cooler's duct needs a tight damper or a cover so the air conditioner does not blow its supply air out through the wet pads all July.

What typically fails and when

Spring startup

After a winter of sitting, the pan is caked, the pads are dust, the pump is seized and the belt has taken a set. Skipping the spring service is how a cooler becomes a roof ornament.

Mid-season

Scaled pumps, clogged bleed lines, stuck floats and motor bearings. A float that overflows every afternoon finds its way through the roof around the duct curb, and the damage shows up as a ceiling stain in the hallway.

Fall and winter

The danger is not freezing. It is leaving the unit wet and open. A wet pan corrodes the cabinet, and an open duct pours heated air out through the cooler all January. Winterizing means draining the pan, shutting off and draining the water line, covering the unit and closing the damper. Our maintenance guide explains what a proper spring and fall visit includes.

Keep it, combine it or replace it

This is where we tell people not to spend money. Keep it if the cabinet is sound and you use it through the dry months. A pump and a set of pads is the cheapest service in all of HVAC. Combine it if you already own both systems and both work. Replace it with another cooler only if the cabinet has rusted and you genuinely run it every spring. Replace it with refrigerated cooling if the house has no air conditioning and you are living through the monsoon on a cooler alone. The repair-or-replace guide lays out the arithmetic, and financing on approved credit exists if the answer is a new system. And a cooler uses water every hour it runs, which in this city is a real cost.
From the ground you can confirm the water supply is on, the damper is open and the switch is set to pump before fan. That is the whole homeowner list. Roof access, water lines, belts and motors are technician work. Whether the cooler deserves another season needs eyes on the cabinet and the ducts, not a web page.

Evaporative Coolers in the Desert

Water, a pad, a fan and a dry sky. That is the entire machine. Here is why it works from April to June, why it gives up in July, and how to decide whether yours is worth keeping.

Cools by evaporation, not refrigeration

Loses ground as the dew point rises

Pads, pumps and floats wear every season

Keep it, combine it or replace it

Schedule today — we’re here 24/7.

Veteran Owned & Operated

How evaporation cools a house

Why it works in May and fails in August

The parts and what they do

Pads and media

Pump

A small submersible pump lifts water to the distribution tubes. Valley water is hard, and mineral scale collects on the impeller until it stalls.

Float valve

A fill valve, like the one in a toilet tank, that holds the pan level. When it sticks open, the pan overflows onto the roof and into the duct curb.

Motor and blower

Most residential coolers use a belt-driven blower with a two-speed motor. Belts glaze and crack, bearings want oil, and a squeal at startup is the first warning.

Bleed-off or purge pump

A line that dumps a little water continuously, or a pump that empties the pan on a timer, so minerals do not concentrate. Without one, the pads crust white within weeks.

Where you find it in Phoenix homes

Mixing a cooler with refrigerated AC

What typically fails and when

Spring startup

After a winter of sitting, the pan is caked, the pads are dust, the pump is seized and the belt has taken a set. Skipping the spring service is how a cooler becomes a roof ornament.

Evaporative Coolers in the Desert

How evaporation cools a house

Why it works in May and fails in August

The parts and what they do

Pads and media

Pump

Float valve

Motor and blower

Bleed-off or purge pump

Where you find it in Phoenix homes

Mixing a cooler with refrigerated AC

What typically fails and when

Spring startup

Mid-season

Fall and winter

Keep it, combine it or replace it

Evaporative Coolers in the Desert: common questions

Keep reading

Evaporative Cooler Service throughout the Phoenix area

Get an honest read on your cooler

Request service

Evaporative Coolers in the Desert

How evaporation cools a house

Why it works in May and fails in August

The parts and what they do

Pads and media

Pump

Float valve

Motor and blower

Bleed-off or purge pump

Where you find it in Phoenix homes

Mixing a cooler with refrigerated AC

What typically fails and when

Spring startup

Mid-season

Fall and winter

Keep it, combine it or replace it

Evaporative Coolers in the Desert: common questions

Keep reading

Evaporative Cooler Service throughout the Phoenix area

Get an honest read on your cooler

Request service