Radiator fans won’t come on when they’re supposed to

[college man]

Nice diagnostic work so far. With you unplugging the coolant fan switch and the fan coming on tells me that the fan switch
is either having a problem or coolant flow to the sensor. Two options. With a scanner read coolant temp and with an ohm
meter unplug the coolant fan switch connector and check for continuity at the switch when at or above the temp.( The switch is
a break on temp rise) You should have no continuity. Pull the relay disable the fan. #2 Remove the fan switch and put it in a pot with
a thermometer and take the temp to and above the set point check continuity. On this one I would use two jumpers to the meters
leads to keep you safe from burns. Note the water should only go high as the threads. You could also try and clean the connector with
some brake clean just to rid any dirt.