1 Do as the Suzuki man says make sure the screen is clean inside.
2 Air con works in fresh air mode all the time unless recirculate is switched on, it will steam up if you have it on recirculate.
3 You should not have air con on all the time, knocks your mpg down about 3-4 mpg. It should be used for about an hour each week though to keep it lubricated or the seals will deteriate.
4 As it is your first car with air con have you had it serviced? Take a look here...............
http://www.nationwideautocentres.co.uk/index.a sp
for aircon advice, click on air conditionong.