Why Is My Evaporative Cooling Blowing Hot Air?

There’s nothing more frustrating than switching on your evaporative cooling system on a hot Melbourne day only to feel warm air coming through the vents. Instead of the fresh, cool breeze you’re expecting, you’re left with what feels like a giant hair dryer pumping hot air through your home.

The good news is that most causes of this problem are straightforward to diagnose, and many can be fixed easily. In this post, we’ll walk through the most common reasons your evaporative cooling is blowing hot air, so you can troubleshoot the issue or know when to call for an evaporative cooling service in Melbourne.

How Evaporative Cooling Works

An evaporative cooler draws warm outside air through water-soaked filter pads. As the air passes through the wet pads, the water evaporates and absorbs heat from the air. This cooled air is then pushed through your ductwork and into your home. The process is simple but relies on several components working together:

a water pump
filter pads
water distribution system
fan motor

When any of these components fail or underperform, you end up with warm air instead of cool.

servicing a brivis evaporative cooler in melbourne

Common Causes of Hot Air from Evaporative Coolers

Dry Filter Pads

This is the most common culprit we see. If your filter pads aren’t saturated with water, the cooling process simply can’t happen. Dry pads mean the air passes through without any evaporation taking place, so what comes out the other end is just warm outside air that’s been pushed through your ducts.

You can check this yourself by accessing the roof unit (if it is safe for you to do so) and touching the pads. They should be thoroughly wet when the system is running. If they’re dry or only damp in patches, something is preventing water from reaching them properly.

Dry pads can result from several issues, including:

a failed water pump
blocked distribution tubes
pads that have become so clogged with mineral buildup that water can’t penetrate them properly

Water Pump Failure

The water pump sits in the base of your evaporative cooler and is responsible for pumping water up to the distribution system at the top of the unit. From there, water trickles down over the filter pads to keep them wet.

When the pump fails, no water reaches the pads. You might hear the fan running normally, but without water circulating, you’ll only get hot air. Pump failures can happen suddenly, or the pump may gradually weaken over time, resulting in reduced water flow before it stops completely.

Signs of pump problems include:

the unit running but producing warm air
unusual noises from the roof unit
visible lack of water flow when you inspect the system

Blocked Water Distribution System

Even if your pump is working fine, water still needs to reach all areas of your filter pads. The distribution system typically consists of a network of small tubes or a “spider” arrangement at the top of the unit that spreads water across the pads.

Over time, these tubes can become blocked with mineral deposits, particularly in areas with hard water. Melbourne’s water quality varies by suburb, and some areas are more prone to calcium and lime buildup than others. When blockages occur, water may only reach parts of the pads, leaving dry patches where no cooling takes place.

The pump strainer can also become clogged with debris, sediment, or mineral scale, reducing water flow to the entire system.

Float Valve Issues

The float valve controls the water level in your cooler’s tank, similar to how the float in a toilet cistern works. When the water level drops, the float valve opens to let more water in. When the tank is full, it closes.

If the float valve gets stuck in the closed position, the tank won’t refill and will eventually run dry. This means no water for the pump to circulate, resulting in dry pads and hot air. Float valves can stick due to mineral buildup, debris, or simple mechanical wear.

Fan Motor or Belt Problems

Older evaporative coolers use a belt-driven system where a V-belt connects the motor to the fan. If this belt slips, breaks, or becomes loose, the fan won’t spin at the correct speed. Reduced fan speed means reduced airflow through the pads and into your home.

While a broken belt will typically stop the fan entirely, a slipping belt can cause intermittent problems or reduced performance that’s harder to diagnose.

Modern units often use direct-drive motors, which eliminate belt issues but can still fail due to electrical faults, overheating, or worn bearings.

Unit Set to Fan-Only Mode

This one catches people out more often than you’d think. Most evaporative cooler controllers have a fan-only mode that runs the fan without activating the water pump. This is useful for ventilation on mild days or for circulating air when you don’t need cooling.

If your unit is set to fan-only mode, you’ll get airflow but no cooling. Check your controller settings to make sure the system is set to cool mode, not just fan.

Controller or Electrical Faults

Sometimes the issue isn’t with the mechanical components but with the control system. A faulty controller might not be sending the signal to activate the water pump, even when the unit appears to be running in cool mode. Electrical issues can also prevent the pump from receiving power while the fan continues to operate normally.

Environmental Reasons Why Your Evaporative Cooling May Be Blowing Hot Air

High Humidity

Evaporative cooling relies on water evaporating into the air, and this process works best when the air is dry. On humid days, the air already contains a lot of moisture, which limits how much additional water can evaporate. Less evaporation means less cooling.

This is a fundamental limitation of evaporative cooling rather than a fault with your system. On muggy days, your cooler may struggle to lower the temperature noticeably, and the air coming through may feel lukewarm rather than cool.

Melbourne’s climate is generally well-suited to evaporative cooling, but we do get humid spells, particularly during summer storms or when tropical air masses move south. On these days, your evaporative cooler simply won’t perform as well as it does on hot, dry days.

Extreme Heat

On extremely hot days, your evaporative cooler has to work harder. While these systems can reduce air temperature by 10 degrees or so, if it’s 42 degrees outside, you might still end up with air around 30-32 degrees coming through your vents. This can feel warm compared to what you’re hoping for, even though the system is actually working correctly.

What to Check Before Calling for a Service

Before calling for an evaporative cooling service in Essendon or other inner Melbourne suburbs, there are a few things worth checking:

Make sure your controller is set to cool mode, not fan-only. This simple oversight is surprisingly common.
Check that the water supply to your cooler is turned on. There’s usually an isolation tap either on the roof near the unit or in your ceiling space.
If you can safely access your roof unit, check whether the filter pads are wet. If they’re dry, you’ve confirmed there’s a water supply or pump issue.
Listen for the sound of the pump running. You should hear a distinct humming or buzzing sound from the pump in addition to the fan noise.

When to Call the Team at ExtrordinAir

If your evaporative cooler is blowing hot air or not performing as it should, ExtrordinAir Heating and Cooling can help. We service, repair, and install all major evaporative cooling brands including Bonaire, Braemar, Breezair, Coolair, and Brivis.

With over 20 years of experience and fully licensed technicians (ARCTick Licence AU29403, VBA Licence 43459), we’ll diagnose the problem and get your system running again quickly.

We service homes across Melbourne’s inner north and western suburbs. Whether you need evaporative cooling installation in Keilor East, or an evaporative cooling service in Pascoe Vale, we are here to help.

Call us today on 1800 407 882 or complete our form below to book a service or request a quote.