The red switch turns the fan on low speed at 16 bar (232 psi), and turns the fan off at 12 bar (174 psi). Pressures above 300psi should have been way more than enough to trigger the fan (that's even high enough to trigger the old green switch, which needed 290 psi). If you can short the leads of the red switch and make the fan turn on low speed, it sure sounds like a bad switch... bad news is, the system has to be discharged to replace it, then vacuum pulled, and re-charged...
Note: If you are jumping the fan on HIGH speed, using the switch on top of the engine... then check the aux fan resistor. If that's bad, the fan will work on high speed, but not low.
Best regards,