AC Noise?

Hi,have owned my 2001 4.6 for almost 6 years and well not that much gone wrong.However over the last 2-3 days i have noticed when i put the AC on there is a slight noise (Hissing ?) from what seems to be the top of the dash? It almost go's and comes back when you press the accelerator,it's not very loud but it's there and also it does not get that cold? Could this be LOW gas?(had her checked and filled about 3 years back)or is it more likely to be something else?......
P.S the noise go's the second you turn off the AC..

AC needs checking every year if the car is a few years old. It should also be exercised (used) every now and again through the winter to keep it sweet. Would think you have leaked all yor gas out.

Thank you, yes try to use it daily if poss.... so may be all out,do you think it has a leak? or is it poss that with use over 3 years or so i have just used it up???

rob evans said:

Thank you, yes try to use it daily if poss.... so may be all out,do you think it has a leak? or is it poss that with use over 3 years or so i have just used it up???

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Top place to look is left hand top of condensor under slam panel where tubes bend down. Condensors (pattern) about £60.00 to £75.00 on fleabay. For genuine ones get a mortgage.