Remove the radiator and clean it out both inside and out. After 20 years, the space between the radiator and AC condenser gets loaded up with all sorts of rocks, dirt junk etc. Also straighten out any bent fins and have the inside flushed.
http://img.photobucket.com/albums/v242/tjts2/Green%20Mercedes/a8.jpg?t=1274761615

http://img.photobucket.com/albums/v242/tjts2/Green%20Mercedes/a6.jpg?t=1274761644

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CENSORED due to not family friendly words