Jimmy L.,
Thanks,..... but.....I cheated.....I looked at the manual's electrical diagram.

Jumpin' Je.,
This is the ETR to me (there is some confusion in terms) . Controls compressor only (to prevent icing of evaporator).
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=23P1AJKI123U03S7F1&year=1982&make=MB&model=300-SD-002&category=R&part=A%2FC+Evap+Temp+Sensor

PM me your email address and I'll send you the electrical diagram for A/C clutch control (too big a file, since it is PDF, for posting in this forum's format).

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)