As for tax deduction on the repair - if you REPAIR the air-con, then you can claim that cost as a deduction this financial year.
If you REPLACE it - then you would need to depreciate the air conditioner over several years, and add it to the cost base of the property. So when you come to sell, you would have a higher cost base from which to calculate your CGT.
Matt
The last year we have been repairing as much as possible, because it is a current year deduction. It doesn't cost much, and a lot less hassle than getting another.
For us, it is usually washers and dryers.