AC on or off?!!?

Right since first reading this I've been using mine on auto, I've noticed that when on high it stays on full power the if you drop it down to 28 it drops slightly but that's it! Also whenever ignition is turned on it comes on full power and weirdest of all is it seems to increase in power along with speed!
Now I have a courtesy car at mo a a3 62plate and the climate in that is totally different! On auto on high is starts low and gradually speeds up when warm then when knocked down it drops a lot until temp in car drops! And it doesn't adjust with speed so does this mean mine is faulty??
 
If its not used for a long period of time isn't unhealthy for the gas and seals,
someone told me regularly use the a/c it will last longer?

Yes it should be used all year otherwise it will leak through the seals and the gas won't be effective...