Why don't you connect them directly to 12V, that way both will do max RPM possible?
Because if the controller doesnt see the fans the machine shuts down and will not hash. Honestly if you ut the PWM line and it is still not speeding up you most likely have a bad fan.
But why don't you leave pwm wiring connected just connect directly to 12v other 2 wires... It should send max rpm to controller, so it should still mine... But the rpm would me maxed..
Am I missing something?