Air conditioning troubleshoot

[mos]

Hi,

I am currently trying to recharge my air conditioning system with the kit you get out of Halfords and it hasn't really worked. I have come up with the following symptoms.

When the car is idling and the a/c is working on its max setting the gauge indicates in the blue which means it is at the correct pressure, however when the accelerator is pressed the gauge falls to green(low)and the low pressure kicks in and the clutch disengages the pressure then rises into the yellow and the clutch engages again and the pressure starts to drop and this cycle continues.

I would gather from this that the system still needs more pressure but my only concern is that when the engine is switched off the gauge rises well into the red zone and i don't want to add more refrigerant if this will damage anything.

Is this rise normal and does it still need more pressure?

Its a ford focus 1.6 2000

Thanks for the help.