If the repair quote is more than half the cost of a new system and your aircon is past the halfway mark of its expected life, replacement is almost always the smarter call. That’s the rule of thumb. The detail behind it is what actually makes the decision easy or hard.

Here’s how we work through this with homeowners on a quote visit, including the real costs of common repairs, the age bands where the maths tips one way or the other, and the situations where the obvious answer turns out to be wrong.

The 50% rule, explained properly

The basic principle: if a single repair quote exceeds 50% of replacement cost, and the system is past the midpoint of its useful life, replacement is the better long-term call.

A worked example: a 10-year-old ducted system needs a $3,500 compressor replacement. A new equivalent ducted system is $11,000 installed. The repair is 32% of replacement cost, but the system is past its midpoint and other components are aging. This is the classic close-call scenario where the answer depends on the rest of the system’s condition.

A clearer example: an 8-year-old split system needs a $300 capacitor replacement. New equivalent system is $3,500 installed. The repair is 9% of replacement cost. Repair, every time.

Another clear one: a 16-year-old ducted system needs a $4,000 indoor fan motor and refrigerant leak repair. New system is $11,000 installed. Repair is 36% of replacement cost on paper, but the system is well past its useful life and the next failure is months away. Replace.

The 50% rule is a starting point, not a substitute for thinking about the whole picture.

Age is the biggest single factor

Most modern split and ducted systems last 15 to 20 years with proper servicing. The age band the system falls into changes the calculation significantly.

0 to 5 years: repair almost always wins. Most systems are still under warranty for major components (compressor warranties are typically 5 to 7 years on quality brands). The rest of the system has years of useful life ahead of it.

6 to 10 years: repair usually still makes sense for anything other than catastrophic failures. The system has half its life left, and replacing it now means walking away from years of useful service. Major component failures (compressor, indoor fan motor) get scrutinised more carefully, but most repairs are worth doing.

11 to 14 years: the genuine grey zone. Decisions become case-by-case. A small repair on a well-maintained system can extend life another 3 to 5 years. A major repair on a system that’s been hammered with no servicing is usually throwing good money after bad.

15+ years: replacement almost always wins. The components are all aging together. Once one major part fails, the others aren’t far behind. Putting a new compressor into a 16-year-old system often means the indoor fan motor goes 18 months later. Modern systems are also dramatically more efficient, so the running cost savings start paying back the replacement cost from year one.

Repair costs by component

Worth knowing what each common repair actually costs, because the language can be vague when you’re looking at a quote.

Smaller repairs (usually worth doing on most systems):

Capacitor or contactor: $80 to $300. Common, quick, almost always worth repairing.

Thermostat or controller: $150 to $500 depending on system and zoning compatibility.

Refrigerant top-up after a leak repair: $300 to $800 depending on system size and how much gas needs replacing. Topping up without finding the leak is bad practice.

Drain line clear or drain pan replacement: $150 to $500.

Fan motor (outdoor condenser fan): $400 to $800.

Larger repairs (worth scrutinising before approving):

Indoor fan motor (ducted system): $600 to $1,200.

Compressor: $1,500 to $3,000+ depending on system size. The single most expensive common failure, and the one most likely to push a borderline system into replace territory.

Evaporator coil: $1,000 to $2,500. Often comes with associated work because the coil failure usually means refrigerant has been lost too.

Condenser coil: $1,200 to $2,800.

Major ductwork replacement on a ducted system: $2,000 to $6,000+ depending on extent.

A repair quote that’s a single line item without any of this detail is worth pushing back on. You should be able to see what’s being replaced and what each part costs.

When repair makes sense

The situations where repair is almost always the right call:

The system is under 7 years old. Most of its useful life is still ahead.

The repair is under $500 on any system. Even on older systems, this is usually worth doing while you plan a replacement on your own timeline rather than under emergency conditions.

The repair is covered or partly covered by warranty. Daikin, Mitsubishi Electric, Fujitsu and Panasonic compressors typically carry 5 to 7 year warranties on quality models, with the parts covered even when labour isn’t.

The system has been properly maintained and is otherwise in good condition. A 12-year-old system with a perfect service record is a different proposition to a 12-year-old system that’s never been touched.

You’re planning to sell within 18 months. A working repaired system gets you across the line; a new system you’ll never recoup the cost of.

Budget constraints make replacement genuinely impossible right now. A repair that buys you another season is sometimes the right call, even if it’s not the most economically optimal one over a 5-year horizon.

When replacement makes sense

The situations where replacement wins on the maths:

The system is over 12 years old and the repair quote is over $1,500. The remaining useful life isn’t long enough to recover the repair cost.

The compressor has failed on a system over 10 years old. Compressor replacement on an older system rarely makes financial sense.

You’ve had multiple repairs in the last two years. The system is telling you what it wants to do.

Energy bills have climbed noticeably without a corresponding usage increase. Modern inverter systems are 20 to 40% more efficient than non-inverter systems from a decade ago, and that pays back genuine money over the system’s life.

The system uses R22 refrigerant. R22 has been phased out and is expensive when it can be sourced at all. Major repairs to an R22 system that involve the refrigerant circuit are usually a poor investment.

You’re staying in the home long-term. The replacement pays back over 5 to 10 years, and you’ll see the return.

You’ve extended or renovated the home and the existing system is undersized. Adding capacity to an undersized system is usually more expensive than replacing it with a properly sized one.

Total cost of ownership matters more than the upfront number

The mistake most homeowners make is comparing the repair quote to the replacement quote and choosing the lower number. The right comparison is what the next 5 to 10 years actually costs.

A repair that buys you 18 more months on a tired system, followed by another repair, followed by an emergency replacement during the first heatwave of summer, is usually more expensive end-to-end than a planned replacement now. Modern inverter systems running at 20 to 40% better efficiency save real money on the power bill (a few hundred dollars a year on a typical Sydney home), which goes some way toward offsetting the replacement cost over a decade.

The other thing the upfront comparison misses: a new system comes with a fresh manufacturer warranty (typically 5 years on the full system, 5 to 7 on the compressor). A repaired old system comes with no warranty on the parts you didn’t repair, which are statistically the most likely things to fail next.

How to actually decide

If you’re looking at a quote and unsure, the process is:

Confirm the age of the system from the data plate on the outdoor unit. Most plates include an installation or manufacture date.

Check what’s actually being repaired and what the parts cost (push back if the quote is a single line item).

Calculate the repair as a percentage of new system cost. Get a replacement quote in parallel so you have a real number to compare against, not a guess.

Factor in the system’s service history and how it’s behaved over the last few years. Multiple repairs in recent memory point to replacement.

Think about how long you’re staying in the home. Long-term means replacement maths usually works. Short-term changes the answer.

If the decision is still unclear, ask the installer for an honest read. A good installer will tell you the system has years left if it does, and will tell you replacement is the smarter call when it is. If the answer always seems to be “replace”, the advice is worth a second opinion.

Frequently asked questions

How long does an air conditioner last in Sydney conditions? With annual servicing, 15 to 20 years for both split and ducted systems. Coastal homes (within 1km of the surf) see faster outdoor unit corrosion and may need replacement closer to 12 to 15 years.

What’s the most expensive component to replace? The compressor. $1,500 to $3,000+ depending on system size, and the single most common failure that pushes a system into replace territory.

Can regular servicing extend the life of my aircon? Yes, significantly. Most premature failures we see are on systems that haven’t been serviced in years. An annual service typically adds 3 to 5 years of useful life.

Is it worth repairing a 15-year-old aircon? Almost never, unless the repair is very minor (under $300). The remaining useful life isn’t enough to recover any meaningful repair cost.

How much more efficient are new systems? Modern inverter systems run 20 to 40% more efficient than non-inverter systems from a decade ago. On a typical Sydney home running aircon for half the year, that’s a few hundred dollars a year on the power bill.

What if my aircon fails during a heatwave? Get a tech out as quickly as possible, but understand that during peak demand most installers are booked out for repairs and even longer for full replacements. The best move is to make this decision before summer hits, in autumn or early spring when there’s actual capacity in the diary.

Are financing options available for replacement? Most reputable installers offer interest-free or low-interest finance options on replacement systems. Worth asking at quote stage, particularly if the choice is between a repair you can’t really afford and a replacement that’s similar money over 24 months.

Can I just replace the outdoor unit? Technically possible but rarely the right call. Modern outdoor and indoor units are designed to work as a matched pair, and mismatching them costs efficiency, voids most warranties, and creates ongoing reliability issues. If the outdoor unit is dead, replacing the full system is almost always the better answer.