A static pressure reading of 75 psi (on both the low and high side) while the clutch is not engaged is not abnormal (depending on under-hood temperature).
If the low side pressure remains at 75 psi when the clutch engages and does not drop, the compressor internals are either a) shot or b) not turning due to a failed clutch (it only looks like the compressor is being turned. Use an inspection mirror to closely watch the center nut/bolt to see if the compressor shaft is actually turning.
Steve
