Aircon gas top-up vs chemical overhaul: what each one costs

If your aircon isn’t performing the way it used to, the fix is usually one of three things, a gas top-up, a chemical wash, or a full chemical overhaul, and they’re priced very differently because they involve very different amounts of work.

The three jobs, and what separates them

Gas top-up. The technician checks refrigerant levels and tops up the gas if it’s low, usually a sign of a slow leak somewhere in the system. This is the quickest of the three jobs.

Chemical wash. The indoor fan coil unit is dismantled and each component washed with a chemical solution to strip out built-up dirt, mould, and grime that a routine service can’t fully reach. No gas is involved.

Chemical overhaul. The most thorough option, both the indoor and outdoor units are dismantled, cleaned, and reassembled, often paired with a gas top-up if needed. This is the job to reach for when a unit hasn’t been deep-cleaned in a long time or performance has dropped noticeably.

Job	What it involves	Relative cost
Gas top-up only	Check and refill refrigerant	Lowest
Chemical wash	Dismantle and clean indoor unit only	Mid-range
Full chemical overhaul	Dismantle, clean, and reassemble both units, gas as needed	Highest, often close to double a wash

What pushes the price up within each job

Unit size and type matter across all three. A small unit under roughly 9,000 BTU is the cheapest to service. A standard-sized split unit sits in the middle. Large or ducted systems cost more because there’s simply more to clean, more refrigerant to check, and more components to reach.

How to tell which one you actually need

Weak cooling with airflow that still feels normal usually points toward low refrigerant, a top-up job. Airflow that’s noticeably weaker even though the unit looks clean, or a musty smell when it runs, points more toward a build-up that a chemical wash would clear. If it’s been over a year since a deep clean and you’re seeing both symptoms, a full overhaul is worth discussing.

A technician who checks before recommending, rather than defaulting straight to the most expensive option, is the one worth trusting with the job. Ask them to explain what they found and why they’re recommending a specific service before you agree to a price.

A leak that keeps coming back

If your unit needs a gas top-up every few months, the top-up itself isn’t the fix, it’s masking a leak that hasn’t been found. Ask specifically for leak detection rather than repeating the same top-up on a schedule, it costs more upfront but saves you from paying for gas that keeps escaping.

Questions to ask before booking either job

Before agreeing to any of these three services, ask the technician to explain what they found that led to the recommendation, not just what the job costs. For a top-up, ask whether they checked for a leak or just refilled the gas, a top-up without a leak check is a temporary fix at best. For a chemical wash or overhaul, ask whether both units will be fully dismantled or just surface-cleaned, since the depth of the clean is what justifies the higher price.

Timing these jobs around your servicing schedule

A chemical wash or overhaul doesn’t need to happen on every routine visit, most units need one roughly once a year or two depending on how heavily they’re used and how humid the space is. Pairing an overhaul with a scheduled servicing visit, rather than treating it as a separate emergency booking, often works out more convenient and sometimes cheaper, since the technician is already on-site and set up for the work.

Matching the job to the actual symptom is the single best way to avoid overpaying for aircon maintenance. You can compare contractors handling this work on our aircon gas top-up and chemical overhaul hub, see our scoring method, or return to the homepage for the full category list.