In case you are reading this, you have a real concern for your cat. Cats are different from dogs as they do not like to change their surroundings every now and then. Dogs love being with their owners and are adaptable. In the case of cats, this does not appear to be the case. You might have taken notice of the fact that your cat leaves you alone when it would be hungry. Cats are self-reliant but in no way, it means that a cat can survive without your help. Suppose you are out on a vacation you can install a cat air conditioner to help your cat. But there are other steps that would put your cat at ease.
Rely on help
Feel no degree of shame in asking for help. The close friends who also own a pet at their homes would not shy away from help. In every couple of days, someone could pop over to see on how the cat would be doing. If you do not have a water fountain the person should refill the water. Cats are solitary creatures and disturbance would be the last thing at the back of their minds. The person whom you assign this task has to be familiar with your cat. If a stranger comes they will scarce the cat and this would not be good.
The doors need to be open
It does not mean the doors of the home, but inside the home, all the doors have to be open. You can put a chair at their entrance so that it does not close on its own. In case if you do not adopt this stance there would be a strong chance where you cut off the cat from the supply of water and food.
Let cat play
There seems to be a perception that cats like to sit around the whole day and do nothing. Another school of thought would be that they like to sleep for long hours. This does not seem to be the case. It would be prudent on your part to leave some toys behind so that the cats can play. Leaving behind an old set of clothes would seem to be a noble idea. This means that the cat could smell it and have a sense of security that you are inside the home.
To switch off the AC unit does seem to be a tricky choice for most homeowners. Could your cat get sick from an air conditioning unit? In case if the vacation time happens to be winter then leave the AC unit on. If it appears to be summer months, it would all depend upon the cat. You could also consider in switching off the AC as the old cats are known to have a slow metabolic rate. If the health of your cat would be good no harm in turning off the AC unit.