hi. do you know for sure it needs to be filled? has it been tested? if your not low and theres actually a different problem with the system you can actually damage the system by over pressurizing it. your best bet is to have someone check the system and see what the problem is. also if it is low you probably have a leak and i believe when they test the system recover/refill they can add a dye so they can trace any kind of a leak you might have.