If it worked right after being serviced then it's slowly got worse I would say you have a leak somewhere.
As far as it not working well right away then becoming colder as you drive this is normal AC operation. All the cold air is soaking up all the heat in the lines and ducts. It needs everything to get cooled off before that icy cold air actually blows out the vents on to you.
As far as it not working well right away then becoming colder as you drive this is normal AC operation. All the cold air is soaking up all the heat in the lines and ducts. It needs everything to get cooled off before that icy cold air actually blows out the vents on to you.