Cleaning suggestions for the indoor air handler of split system air conditioners, window air conditioners, and through-wall air conditioners & heat pumps.

This article describes simple cleaning procedures to remove mold from the air path of window or wall mounted indoor air conditioning or heat pump units.

This article series describes split system air conditioning & heat pump systems. We review the major system components, switches & controls, and typical applications for split system cooling systems. We also discuss use of the remote thermostat control, where to find and how to clean the split system air filters, how condensate is disposed-of, and what to check first if your split system air conditioner is not working properly.

Cleaning Mold from a Wall or Window-Mounted Air Conditioner

These air conditioner mold removal steps will work on most window or through-wall air conditioners as well as on wall-mounted split system air conditioners and heat pumps.

A split system or "ductless" air conditioning (or A/C & heat pump) system dispenses with duct work entirely, using a wall-mounted indoor evaporator/blower unit and a separate outside compressor/condenser (below left and right).

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[Click to enlarge any image]

At above left you can see rather typical dark mold growth on the plastic surfaces of the indoor half of a wall-mounted split system air conditioner. Similar mold may appear on window or through-wall mounted air conditioners as well.

Mold grows readily on the plastic surfaces of the air conditioner's face cover and on its air-directing louvers because these surfaces often are damp with condensate from the conditioned air.

Mold may also grow on the metallic surfaces of the squirrel cage fan that blows room air through the air conditioner, more so as those surfaces accumulate building dust that typically includes organic debris such as skin cells.

At left is a close-up of a fairly-clean split system air conditioner blower fan.

If you click to enlarge the image you'll see normal dust accumulation on the blade edges. In contrast, if the curved blades have become dust-laden not only does that serve as possible mold food it also means that the air-flow of the blower fan will be reduced.

Don't panic if you see some black mold or dark brown mold in the blower portion of your wall-mounted split system air conditioner. Most commonly the fungus is a member of the Cladosporium sp. family (among those samples we've tested in our lab).

Molds found in buildings may be relatively harmless, or allergenic, or sometimes more seriously harmful. Health risks are greater for people at extra risk themselves such as asthmatics, people suffering from allergies, the elderly, infants, and people with a compromised immune system.

It is normal for dust and debris to collect on the fins of air conditioner air direction louvers, grilles, and squirrel cage blower fans. Typically this is harmless house dust and it's not a problem until it obstructs air flow.

Below is a fairly dirty air conditioner air outlet grille or fan blade.

But if the air conditioner is frequently wet, for example from condensate, that same dust can host the growth of a variety of molds, many of which are not highly dangerous.

However depending on the surface material that has been wet, sometimes different and more troublesome mold genera/species may grow.

And if such areas in the building are large (more than 30 sq .ft. of contiguous mold) or if harmful molds are in the air path of building air handlers such as air conditioners, professional cleaning may be in order.
S

ee MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD if your building has a significant mold problem.

All of these surfaces can be cleaned if you work carefully to avoid damaging cooling coil fins or knocking about the wall mounted unit and its components.

You'll need some household spray cleaner (any cleaner will work but avoid using corrosive cleaners or agents on metal parts and avoid spraying your eyes). You'll also want some clean rags or paper towels and a clean soft bristle paint brush.

Remove the plastic cover for the air conditioner and for best results, use your spray cleaner, paint brush, and a garden hose sprayer outdoors to clean the cover and its louvers.

You can do that job indoors too at a large kitchen sink. Now while the air conditioner's cover is drying there is more mold cleaning to do.

Watch out: be sure that electrical power is off and disconnected from your air conditioner before removing its cover for cleaning or service. Otherwise you risk death by electrocution or cut or amputated fingers by moving parts should the equipment start while you're messing with it.

While the covers are off of the indoor air handler unit of a split system air conditioner, if you take care not to bend or damage any components, the use of a simple household spray cleaner, paper towels, and a paint brush can clean out most of the mold that likes to grow on these frequently-damp surfaces in the air conditioner's room-air path.

Using spray cleaner and dry paper towels we sprayed and wiped clean the easily-accessible areas of the wall-mounted air handler's surfaces taking care not to move, disturb, or break any louvers or other components. You can see the black mold on our paper towel at above left.

We also used a household-cleaner to wet our long soft bristle paint brush that in turn was used to gently clean the louvers of the blower fan (above right).

Rinse the paint brush in clean running water, wet it again, and go back to continue cleaning the louvers of the squirrel cage blower fan until accumulated dust and debris have been removed.

Watch out: take care not to spray or wet electrical components, and avoid spraying or wetting any fan bearings or you may be sorry you undertook this step.

Watch out: if the cooling coil itself is badly soiled or blocked with dust and debris at your air conditioner or heat pump that tells us two things:

1. You should as for cleaning help from a professional who can probably get the job done faster, more completely, at lower cost, and with less risk of damaging the equipment than if you mess with it yourself.
2. You have not been cleaning the unit's air filter as frequently as you should.

At above-left is rather typical dark mold growth on the plastic components of a wall-mounted air conditioner.

This mold growth is small in total area, is not deserving of panic, and would be of only trivial concern were it not in the air path of an air conditioner that circulates room air.

You indeed might want to clean the system using the methods described in the article above, particularly if there are building indoor air quality complaints that appear to correlate with operation of the air conditioner.

Clean the Split System Air Conditioner Filters Too

While you're cleaning up your split system air conditioner to remove mold from the blower assembly it makes sense to also remove and clean the unit's air filters.

Depending on brand and model the air filter location and removal process varies.

You may need to snap open a cover to remove the filters (like the Sanyo unit we show below), or the filter may pull out of a slot in the split system's room air unit.

In either case nearly all split system air conditioners and heat pumps use filters that are designed to be simply washed clean in warm water, dried, and returned to duty.

If we see actual mold growth on this filter we'd use a household spray cleaner that provides a dilute bleach solution, taking care to rinse the filter thoroughly to remove all of the bleach before returning the filter to service.

But in normal circumstances the filter will simply wash clean using warm water as I'm demonstrating above.

Question: How to prevent mold growth in a split system or other air conditioner

I am about to purchase a new mini split because my old one broke and has mold. Do you know of a method to prevent mold from growing in the first place? - anonymous by private email 2018/10/24

Reply:

I have not found a mold-proof air conditioner or air handler, and I often find mold growing on the organic debris that is deposited on air filters and on the plastic or metal surfaces in the air path.

Here are some things that will at least reduce the rate of mold growth in air conditioning and air handling equipment:

• Size the unit properly so that it will properly de-humidify the building air
• Watch the condensate drain system to keep it working and to be sure excessive condensate isn't blowing past the condensate drip tray and into the duct system or for a mini split, blowing out onto the air distribution vanes
• UV light: Some commercial air handler service techs experiment with the addition of UV light to try to bathe mold-prone surfaces in constant UV to retard mold growth.
  
  UV won't kill off organisms in air blowing rapidly through the air handler but it can treat AHU surfaces.
  
  UV Light Disinfection of HVAC Ducts & Air Handlers is discussed
  
  at AIR FILTER OPTIMUM INDOOR
  
  Using UV light in a wide range of applications inculding the control of bacteria, mold, and algae or moss growth is also discussed
  
  at UV LIGHT BLACK LIGHT USES
• Change the air filter or for a mini split take out and wash the air filters regularly - monthly is recommended.
• Review the building for sources of abnormally high humidity, leaks, or existing mold reservoirs - those conditions can exacerbate mold growth in various other building areas and in building mechanical equipment.

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Continue reading at SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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