Common air conditioning installation mistakes in Australian homes and how to avoid them

The most common air conditioning installation mistakes in Australian homes are choosing the wrong size, placing the indoor head where it blows on people or misses the room, putting the outdoor unit where it is noisy, hot or hard to service, condensate drains that leak or drip on paths, poorly insulated or crushed ducts in ducted systems, and electrical work that was not planned. Almost all of them can be prevented at the quoting stage by asking the right questions and getting the answers in writing. This guide lists each failure, what it looks like and how to avoid it. It is part of where to get help.

Mistakes, symptoms and prevention

Mistake	What you notice	How to prevent it
Undersized unit	Room never reaches set temperature on hot or cold days	Ask how capacity was chosen (sizing guide)
Oversized unit	Uneven comfort, higher cost, cycling	Same — a load assessment, not a guess
Head above a bed or couch	Cold draughts on people in summer	Agree head location on a floor sketch
Head in a corner or behind a beam	Part of room stays hot or cold	Ask how air will circulate
Outdoor unit under a bedroom window	Noise at night, neighbour complaints	Agree location; check noise level
Outdoor unit in direct afternoon sun or enclosed space	Lower efficiency, overheating	Allow airflow clearances per manual
Condensate drain on a path or into a garden bed against the slab	Slippery paths, damp walls, termite risk	Route condensate to an appropriate drain
Condensate falling back (poor fall)	Water dripping from the indoor head	Correct fall or condensate pump
Wall penetration not sealed	Draughts, pests, water entry	Ask for sealing and capping
Refrigerant leak at joints	Loss of performance after months	Licensed technician, pressure testing (licence guide)
Ducts crushed, kinked or poorly insulated	Weak airflow at outlets, high bills	Specify duct insulation rating and inspect roof space
Return air too small	Noise, poor airflow, ducted unit struggles	Ask for return air sizing
Unplanned switchboard work	Surprise extra charge on the day	Assess the board at quote stage (switchboard guide)
Outdoor unit on unsuitable brackets	Vibration, noise, safety risk	Ask for bracket type and wall fixing
Coastal corrosion	Rust on outdoor unit within a few years near the sea	Ask about coastal protection and warranty exclusions

Split systems: getting placement right

Placement decides comfort and noise more than brand does.

Indoor head:

High on a wall with clear airflow along the room's longest dimension.
Not directly above beds, desks or the main couch.
Clear of curtains and cupboards that would block return air.
Within a sensible distance of an outside wall to keep the pipe run short.

Outdoor unit:

On a level pad or solid wall bracket with clearances the manual specifies.
Away from bedrooms, yours and the neighbours'.
Out of direct afternoon sun where possible, but never enclosed without airflow.
Accessible for servicing.

Illustrative cost of fixing later: moving a split system after installation means recovering refrigerant, new pipework, patching walls and reconnecting power. That can cost a large share of the original install; getting the location right first time is much cheaper.

Ducted systems: the hidden failures

Ducted systems fail quietly in the roof space.

Duct insulation. Ask for the duct insulation R-value in the quote. Hot roof spaces in summer can add significant heat to ducts.
Duct routing. Long, kinked or crushed ducts reduce airflow. Ask the installer to inspect after installation and offer you photos of the roof space.
Zoning. Too many small zones can starve the system of airflow when only one zone runs. Ask how the system handles minimum airflow.
Return air. A return grille that is too small causes noise and poor performance.
Controller location. A wall controller with a temperature sensor placed in a sunny hallway or near a kitchen can misread the house.

The ducted versus split guide explains when ducted is the right choice in the first place.

Hot water installations

Heat pump water heaters have their own installation problems: noise near bedrooms, drain lines not connected, tempering valves missing, wrong tank size and timers set to peak tariffs. See heat pump hot water problems.

A day-one inspection list

After installation, before final payment:

Each unit heats and cools as expected.
Indoor heads level; no water dripping.
Condensate drains run to an appropriate location.
Wall penetrations sealed inside and out.
Outdoor unit secure, level and with clearances.
Controllers explained; filters shown.
Electrical and plumbing compliance certificates received.
Warranty documents received and registration explained.
Old units removed and refrigerant recovered.

Use the before-you-sign checklist at the quote stage to prevent most of these.

If a mistake has already happened

Installation is a service covered by the consumer guarantees: it must be done with due care and skill and be fit for any purpose you made known. Write to the installer describing the problem, attach photos and ask for it to be fixed within a reasonable time. If it is not, contact your state consumer agency. See warranties and consumer guarantees and rebate scams if the installation came from a door-to-door offer.

Frequently asked questions

Is some water from the outdoor unit normal?

Yes. In heating mode, outdoor units produce water during defrost cycles. Indoor heads produce condensate in cooling mode, which should drain away, not drip.

Can I ask for photos of the roof space after a ducted install?

Yes. It is reasonable to ask, and it helps if you need to make a claim later.

My split system smells musty. Is that an installation fault?

Often it is dirty filters or coils, which is maintenance. If the drain is blocked or has poor fall, it may be an installation issue.

Who fixes a mistake if the installer subcontracted the work?

The business you contracted with remains responsible to you under the consumer guarantees.

Official sources

ACCC — consumer guarantees for services
Australian Refrigeration Council (ARCtick) — licensed technicians
YourHome — heating and cooling design
energy.gov.au — efficient heating and cooling use