ACC servo help

My '79 450SL (76,000) has no heat. Had the dealer check it out, they said it was the servo. Checking my service records the previous owner had the servo replaced 6 years ago (10,000 miles), for $160.00. The dealer quoted me $1540.00 for the servo and install. Anyone know how difficult this install is? Is it something I could tackle myself if I bought an aluminum servo(better quality) through the MB club for $499.00? Since I only drive it in the summer could I just not fix it? Does the servo affect the air conditioning? Any help would be appreciated. Thanks

sbr