There is a very specific kind of panic that hits around the second week of December. The kids are on holidays, it is 34 degrees, the southerly has not come through, and the aircon that was a bit noisy last summer has finally given up. You ring around and every installer from Manly to Palm Beach is booked until late January.

If you have lived that summer, you know October is when to get ahead of it. Here is the checklist we are working through this year, including a NSW rebate that most Northern Beaches households do not realise they qualify for.

1. Run it now, not in December

Turn the aircon on cold for 20 minutes on the next warm day. If it takes ages to cool the room, smells musty, drips inside, or the outdoor unit rattles, you have found the problem while there is still time to do something about it. October and early November are the quiet months for aircon installers. By late November the good ones are gone until after Christmas.

2. Clean the filters (yes, really)

Pull the front cover off the indoor unit, slide the mesh filters out and rinse them in the laundry sink. It takes five minutes and it is the single biggest thing you can do for running cost. A clogged filter makes the unit work harder for less cooling. Do it again in January.

3. Check the outdoor unit for salt

This is the Northern Beaches problem. Anything from Curl Curl to Avalon that sits within a few hundred metres of the water gets salt spray on the outdoor unit, and the aluminium fins corrode faster than they would in the western suburbs. Have a look at the fins on the back and sides. If they are crumbling or the coil looks furry and white, the unit is losing efficiency and is probably on borrowed time. Newer units come with coated coils for coastal homes, which is worth asking about if you are replacing.

4. Find out what the NSW rebate is actually worth to you

Here is the one that surprises people. NSW has a government energy savings scheme that puts a discount on new and replacement air conditioners installed by an accredited provider. It is not a cashback you claim afterwards. The discount comes off the installed price on the day, and you sign a nomination form with the installer before the work starts.

A few things worth knowing:

• It covers both replacing an old unit and installing a new one where there was nothing before.
• Ducted systems are covered as well as split systems.
• Homeowners, landlords and renters (with the owner’s permission) can all use it.
• The amount depends on the size of the unit and whether it is new or a replacement. For a typical 6kW split system it is a few hundred dollars, more for a replacement than a new install, and larger ducted systems attract more again.
• The unit has to be a high efficiency model approved under the scheme, which rules out the cheapest ones on the market. That is not a bad thing on a coastal house.

You can check what your home qualifies for and get quotes from accredited installers through the NSW air conditioning rebate page. It is an independent site, not a government one, and you put in your postcode and what you have now to see the options. There is a separate section for seniors and concession card holders if you are sorting this out for parents or grandparents on the Beaches.

5. Size it for the room, not the price tag

The most common mistake in Beaches homes is a 2.5kW unit in a north-facing living room with big glass doors. It runs flat out all afternoon and never gets there. A rough guide is 2.5kW for a bedroom, 3.5kW for a small living area, and 5 to 7kW for an open plan kitchen and living space, but sun exposure and ceiling height change that a lot. If you are replacing, ask the installer to size it properly rather than just matching the old one.

6. Book it before school holidays finish

If you decide to replace, get the quote in October and the install booked for early November. Under the scheme the installer handles the paperwork on the day, and most jobs are done within a week of the quote being accepted, so you will be sorted well before the first real heatwave. Leave it until December and you will be doing what we all did last year: buying a pedestal fan from Warringah Mall and hoping for a southerly.

Ready to check? See what your home is eligible for before summer.