http://catalog.peachparts.com/ShopByVehicle.epc?q=1986-Mercedes--Benz-300e-Climate--Control&yearid=1986%40%401986&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6198%3AMBC%7C1507%3AED%7C10000013%40%40300E&catid=242213%40%40Climate+Control&subcatid=242276@@A%2FC+Relay&mode=PA
That's why...
$6 vs well over $100.
But that is still just a guess...it could also be they used the relay by-passed the RPM speed control on the comp feed.... or to activate the aux fan w/comp run signal, etc, etc ,etc......so, you see, until you have the term/wires listed here , me and anyones else is guessing what they did to the stock circuit with the install of that relay..it is THAT simple.