I have a 1998 C230.

My problem occurred a week ago when we were on the highway.
My air conditioning stopped cooling. I set the unit a few degrees lower
and increased the fan speed. This did not help.
I decided to head back home.

After I existed the freeway, about 2 miles on surface streets, it began working again, very well.
I have used the car twice since then. It seemed a little slow to initially cool, but is working fine.
I have not had it back on the highway yet.

Any suggestions would be appreciated.

P.S.
What is a good manual for A/C repair on this car?
I bought the Chilton's version, and it very lacking.