Our '02 300M's A/C seemed to be incapable of producing really cold air.
Then, while my wife was driving it, she said she heard a hissing noise,
and now I detect an oily smell. Seems to me like an evaporator failure
(which I understand was a common problem).

How easy is it to fix this myself? The books and Web sites say to have
the refrigerant recovered professionally first, but I'm guessing that
there's none left anyway.

I saw estimates of $1000+ from a few years ago, but an after-market
evaporator is only $100, a receiver/drier $27, and replacement R134a not
a whole lot.

Somebody reported that the problem on his was merely the Schrader valve.
Where is that located?

Perce