When I bought my 300E in October of 98, I never really tried to run the A/C much (stupid move). It was cool anyway, but as it warmed up in the spring, realized that there was a leak, since I was getting warm air too.
Dealership diagnosed that the evaporator needed to be replaced. That requires the removal of the dash and an expensive unit which totaled $1800 (I guess the previous owner found that out too and cut his losses). Fortunately, I had purchased an extended warranty, so I was out the $250 deductible instead.
I had a really nice Jag convertible that also had the evaporator go out the following year. Quoted about $3000 for its replacement including labor, so I cut my losses and traded it in for the 500SL we now have.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car