Have you set the switch on the the back of the unit to AC?
Just set C and P both to 0.
Select channel 1, hold the Mode button down until 1 flashes on the left, keep pressing the Volume button until 'Set' appears and the then turn the Volume knob until 20 is displayed, then press the Mode button again to exit.
Next hold the mode button down for approx 3 seconds until you hear a beep, '1234M' should be flashing on the left, turn the Volume button and change the Gain to 5, then press the Mode button to exit.
If you have the boost solenoid plumbed in correctly you should now see an increase in boost (if there's no increase in peak boost pressure then either you've not connected the solenoid correctly or there's a problem with the solenoid or wiring). To increase or decrease boost you need to increase or decrease the value for 'Set'. Once you've got a stable desired boost pressure, you can then increase the Gain until the boost pressure overshoots or spikes above the desired pressure, then just back the Gain off until the boost spike no longer occurs.