Last summer, the A/C wouldnt come on so I took it to the dealership and they said it was overcharged. how it became overcharge i have no idea because the A/C has never been touched. anyway, they drained it, refilled it and it ran fine for the summer. now this year it isn't turning on again and i checked the pressure and it is overcharged again. any idea what would cause this? thanks in advance for your help.