To do it correctly, one needs to use a recovery machine (IF any freon's still present?), recover the freon first before removing the old accumlator. Then once the new accumulator's installed, the system needs to be evacuated in order to remove all moisture from the system or you're wasting your time and money on a new accumulator. If not removed, the excessive moiture when mixed with 134a's PAG oil becomes acidic and will then find its way out, like ruin the next costly part, your evaporator.