Hello guys, I'm new here but been researching at your site for a while now. Lotta helpful stuff.
I searched for such problem but couldn't find an exact match to the one I'm having.

I've got a 95 Z28 which overheats because fans don't turn on. Now if I turn my A/C on, both fans will turn on but they will be weak, so I decided to take a look myself at the fan wiring and after messing with it (checked volts and if the cables were properly connected) I noticed that by only leaving the passenger side fan hooked, it'd turn on at full power when switching the A/C on. I checked all the other stuff, water pump, coolant, relays, sensors.. and everything seems to be fine, could the fan gone bad? wiring maybe? Thanks.

 

try jumping the fan relays. if they run really strong, then the fan motors are good. if they are weak, replace them.

 

maybe high speed relay is bad? with the multimeter, also check to see which relay the the PCM is commanding ON and then swap the other relay out for another one and see if it works