I'm in QLD so its pretty hot here, my air con had a few problems when i first got my car, the compressor seized, then when i had the compressor replaced I had the loose wire conections to the fan. [dose your fan cut in and out] , I am beginning to think this is what might have killed the compressor in my car.
Every time the fan would cut out, even for only a second it disengages the clutch on the compressor for a few seconds causing the air-con to turn off for a bit.
This could be happening to you everytime you hit even a little bump in the road. One way to check if the wiring to the fan isn't a tight conection is run the air-con and fan on high for a while, reach under the passenger side of the dash the wiring to the fan is about 10 to 15cm from outer side kick pannel and runs back from the glove box towards the firewall, it's made up of 5 wires 2 thicker and 3 thinner wires, run your fingers along the wiring loom the wires go into a rubber boot, if these wires are really hot like really hot to the point you can't keep your hand there you might have a bad conection, it will be one of the thicker wires conectioning to the fan you will know which one it is it will be all melted. Don't pull anything apart there untill your sure thats it, its a real pain in the neck to get the wires conected back on the fan.
Once i fixed the loose conection the air con keeps up pretty well it's 100% better than it was. Other than that you might need a bit more gas, any good air-con guy can sort it, these cars are really easy to work on so there shouldn't be any reason for ridiculous cost for labour.
If you have poor air flow it could be a blocked pollen filter, its located under the plastic cover at base of windscreen you will need to remove windscreen wipers it get in there.
Cheers Chris.