Another PFC - A/C Fix; no relay required
 

This mod as show is for engines not using ISC idle control, and:
(1) gets rid of the relay that another fix uses
(2) does not require cutting ECU wires.

But if a diode is inserted into the cut ELU wire with it's cathode connected to wards the switch (ground) side, and the ground side connected to the fan resistor, I think it will function fine for ISC controlled engines.