First, remove the aux fan fuse and replace with new one. If this doesn't
work, then you need to run power direct to aux fan to check if it is good.
Once good, then you have to change the single and double prongs thermoswitch
sensors on the engne... by the thermostat. If it still doesn't work, then
check the high pressure switch by jumping the two wires together... you can
do this test earlier too.