Evaporative Cooler Pads: Clean or Replace Before Summer? How to Tell in a Melbourne Spring

Somewhere in the last two weeks of September, Melbourne gets its first afternoon that actually feels warm, and evaporative coolers across the city get switched on for the first time since autumn. What comes out of the vents in the first ten minutes tells you a lot about the pads. That is the point to make the clean-or-replace decision, while there is still time to act on it, rather than on the first genuinely hot day when everyone else has just found the same problem.

The pads are the whole machine, in a sense. An evaporative cooler is a fan pulling outside air through wet media, and the water evaporating off the pad is what takes the heat out of the air. A pad that cannot hold water evenly, or that air cannot pass through freely, cannot cool, no matter how well the pump and fan are running.

What the pads have been through since autumn

When the cooler was shut down for the year, the pads were wet, or at least damp, and carrying whatever the last few weeks of running had left in them. Melbourne water is relatively soft, but evaporation concentrates whatever minerals are in it, and over a summer that leaves a fine deposit through the media. If the tank was not drained at shutdown, the pads dried out slowly with the last of that concentrated water, and the deposit set hard.

Then the unit sat through winter with the dampers closed and the pads dry. Dust and pollen settled into the outer face. Insects found their way in. On roofs under trees, leaf litter collected against the louvres. The pads have also been through months of cold and damp, which is a mixed blessing: dry pads do not grow much, but any biological film that was on the media when it dried has simply been waiting for the water to return.

Reading the first run

Switch the cooler on, let the pump run for a few minutes before the fan if the controller allows it, then run the fan on low and pay attention to three things.

The first is smell. A dusty, slightly stale smell in the first few minutes is normal and comes from the flushed pads. It should fade as the run continues and be largely gone after the tank has been drained and refilled. A sour or mouldy smell that does not fade, or that returns every time the unit starts, is the media holding something and will not clear on its own.

The second is the air itself. It should feel noticeably cooler and slightly humid at the vents within a few minutes of the pads wetting through, even on a mild day. Air that feels the same temperature as outside means either the pads are not wetting or they cannot evaporate water any more.

The third is water. If the unit is accessible and visible, watch how the pads wet. They should darken evenly from the top down, across their full width, within a minute or so of the pump starting. Dry stripes, a dry lower half or a dry corner all mean the water is not reaching that part of the pad. That is often a distribution problem rather than a pad problem, and it is worth sorting before judging the pad.

Pads that will come good with a clean

A pad that is worth cleaning is one where the media itself is still sound and the problem is what is sitting in it. The signs are consistent: the pad holds its shape and sits firmly in its frame, the surface is dusty or discoloured but the honeycomb channels are open when you look through it against the light, it wets evenly once the water is flowing, and the first-run smell fades as it flushes.

Cleaning a sound pad is gentle work. The tank is drained, the sludge and scale are cleared from the bottom of the unit, the distribution tray or trough above each pad is cleared so water reaches the whole width, and the pads themselves are rinsed at low pressure from the inside face outward so debris is pushed out the way it came in rather than deeper into the media. The pads are left to dry fully before the unit is closed up, then the tank is refilled with fresh water and the unit is run to check that every pad wets evenly.

What cleaning should never involve is scrubbing, a pressure washer, or bleach and strong chemical cleaners. Cellulose media is destroyed by all three. A pad that has been pressure-washed looks clean and then collapses or wets unevenly for the rest of its life.

Pads that are finished

Some pads are past the point where cleaning helps, and it is better to know that in September than in January. Look for media that crumbles or flakes when touched, or that has gone soft and spongy rather than firm. Look for a pad that has sagged in its frame, leaving a gap at the top or the side that air can bypass entirely, which means that section of the unit is doing nothing. Look for a heavy white or grey crust of mineral scale, particularly across the top where the water enters and along the bottom edge, which blocks the channels and stops the pad wetting. Look for dark staining or visible growth on the face that does not rinse away, and for a smell that survives cleaning.

The other tell is performance once everything else has been checked: pads wetting evenly, tank fresh, fan moving air, and the vents still barely cooler than outside. The media has lost its capacity to hold and evaporate water, and there is no cleaning fix for that.

Replacement is a straightforward job for someone who is already up there for a service, and it is one of the reasons a proper pre-summer evaporative cooling service looks at the pads rather than just the pump and float. New pads sized for the unit, seated properly in their frames with no gaps, and a clean tank underneath them is essentially a new cooler in terms of what comes out of the vents.

Why the tank and the water matter as much as the pads

It is tempting to treat the pads in isolation, but the water they are fed with decides how long they last. A tank full of last summer’s sediment sends that sediment straight back onto new pads. A pump that is weak or partly blocked wets the pads unevenly, so parts of the media dry out and scale up while other parts are overworked. A distribution tray with blocked holes leaves permanent dry stripes that eventually become dead sections of pad. A drain or dump valve that is not working leaves concentrated water in the unit at every shutdown, which is where much of the scale comes from.

Any pad decision, clean or replace, should come with a clean tank, a checked pump, clear distribution and a working drain, or the new pads inherit the old problems.

Doing it now rather than in December

The practical argument for looking at the pads in September is time. If they only need a clean, it can be done on a mild day with no one in the house missing the cooler. If they need replacing, there is time to get the right pads for the unit and have them fitted before they are needed, rather than discovering the problem on the first hot day when the unit runs all afternoon and delivers warm, musty air.

The other argument is the roof. Most evaporative units in Melbourne sit on the roof, and pulling pads out means being up there, which is not a job for a ladder on a windy day. A technician who is on the roof anyway for a service can assess the pads, clean or replace them, clear the tank and check the water system in one visit, and the first hot day arrives with the cooler ready rather than as a surprise.

Frequently asked questions

What is the smell when I turn the evaporative cooler on for the first time in spring?

Most often it is the pads. They have sat dry since autumn with a summer of dust, insect debris and whatever the last tank of water left behind, and the first flow of water through them releases it all at once. On pads that are otherwise sound the smell fades within the first run or two as the media is flushed. A smell that persists after the tank has been drained and refilled and the pads have run wet for a while is a sign the media itself is holding something, and cleaning or replacing the pads is what ends it. A sharp, mouldy smell that comes with visible growth on the pad face is a replace, not a clean.

Can I clean the pads myself?

The part that is genuinely a home job is the tank: draining it, clearing the sludge and refilling with fresh water. The pads are more delicate than they look. Cellulose media is damaged by scrubbing, by a pressure washer and by bleach or strong cleaners, all of which shorten its life or ruin it outright. A gentle low-pressure rinse with the pad out of the unit, from the clean side through to the dirty side, is about as far as home cleaning should go. The other limit is where the unit is. Most Melbourne evaporative coolers sit on the roof, and getting up there to pull pads out is not worth the fall risk. Power must also be off at the isolator before anything is removed.

The pads look fine but the cooler is not cooling much. Is it still the pads?

Possibly, but check the water first. A pad that is not being wetted evenly cannot cool, and the usual reasons are a blocked distribution tray or trough above the pad, a pump that has weakened or blocked over winter, a float valve that is not letting the tank fill, or a tank that is draining before the water has a chance to circulate. Dry streaks on a pad while the unit is running point straight at the water distribution rather than the pad itself. Once the pad is wetting fully from top to bottom and the cooling is still poor, the media has lost its ability to hold and evaporate water and it is time to replace it.

Do all the pads need replacing at once?

Usually yes, and for a practical reason rather than a rule. Pads in the same unit have had the same water, the same dust and the same number of seasons, so when one has reached the end the others are rarely far behind. Mixing one new pad with three old ones also makes the unit cool unevenly, because air takes the path of least resistance and flows through the pad with the most open channels. The exception is a single pad that has been physically damaged, by a branch or a bird for example, while the rest are sound.