Mazda Repair: 2005 mazda mpv ac problem, 2005 mazda mpv, freon gas

Question
I have a 2005 mazda mpv. I have been having problem with my airconditioning unit and have been desperate to find someone who can help me fix it. My ac is not cooling enough, I've tried putting freon gas but it will only keep cooling for two weeks and then it declines slowly. One mechanic say i have a leak in my system, he tried to put freon with dye but could not see any stain afterwards, then he placed STOP LEAK freon hoping to clog the leak but it didn't work as well. Another mechanic suggests to vacuum the whole system so he can find where the leak is but is afraid to use his vacuum equipment because he's afraid the leak stop ingredients placed in my Ac will damage his machine. I also tried to clean the air filters at the back of my globe box. I also noticed that the fan is not that powerful enough. Is there a way to to improve the fan's strenght.I don't want to bring it to Mazda dealer for i surely with spend a lot of money.Please help me.

Answer
the fan has base setings and can't be changed however if it the ac gets better after recharging it then slowly losses it's cooling affect thats a key sign there is a leak your going to have to have the leak fixed relessing feon is hardful and recharging the system all the time can get costly.