The "KLIMA" relay is located directly behind the battery. In my car there is a thin black piece of plastic right behind the battery that is held in place by the formed rubber gasket that seals between the hood and the engine compartment at the firewall. If you raise the hood to the 90 degree position, this rubber gasket lifts off the firewall, and then the plastic shield also lifts out. The "KLIMA" relay is about an inch thick, and two inches wide and two or three inches tall. It is a black plastic box, and has the words "KLIMA 4 ZYL. 12 V" in fairly large white letters on the top. It sits behind a relay, same basic size and shape, that says "4 ZYL 7100 min KVS" on the top.
I took out both of the relays and cleaned them and then put them back in. The pull out vertically and have the ususal Mercedes-Benz array of silver plated eighth inch diameter pins on the bottom. They were a little hard to pull out, mainly because there is not much room to get a good grip on them in the little cubby hole they sit in.
Good Luck. Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)