I was even more surprised than you Sam. I use a small (170L) dead Kelvinator fridge for a single fermenter. 2x1.25L bottles of frozen salt water brings the inside temp down dramatically, even on 30C+ days. So much so that my latest brew (an ale) was brought down to 10-12C with the ambient temp in the fridge sitting on 15C. The bottles were resting on the side of the fermenter.
I've since changed to using a single bottle and temps have risen to 15C brew. I hope it doesn't spoil the Aussie Pale!