98 EB SOHC, AC problem

My AC was not very cold so I took it to the dealer and they said the
accumulator and cycling switch were both rusted and probably causing a leak.
What would cause that - I though the AC system had lots of oil in it to
prevent rust? The same dealer fixed it last year by simply adding a lb of
refrigerant (they said they couldn't find a leak) and now they want a ton of
money to fix it.

Comments?

--
Allan Williams