On the 83 300SD there should be two switches on the R/D.
One (black with two prongs) is a low pressure cut off switch to protect the compressor should refrigerant leak out.
The other is typically red (although green, a different pressure setting, is also available) with pigtails coming of it. This is the switch that turns on the aux. fan when the high side pressure reaches a set amount. It sounds like the P.O. did not insert this switch into the new R/D, but merely jumpered the two wires to it, keeping the aux. fan constantly on. ?
