A4 AC over gassed

Please can you give me your thoughts on this:

The ECON light came on permanently indicating fault with AC, so i think may aswell get the gas renewed as nearly 4 years old and never been changed. The car is a A4 2005 3.0L V6 TDI S line, so take along to local garage their machine has options to set the car make model into it and it will sort out quantities of gas, oil etc itself. It thinks it needs 500g of gas. So it pulls out 820g of old gas (no more so not a leak). So the mechanic and i look in the book and it says for a A6 it can be 800g so he changes the machine manually to put 800g back.

When finished ECON light still on, so he plugs in their diagnostic fault reader and it comes up with the following fault code "00819 High pressure sensor - G65 open circuit" So its concluded the sensor is faulty and needs renewing.

After reading a few posts on here i find that the correct quantity of gas is labelled up on the underside of the bonnet. This reads 500g +- 20g.

I assume that therefore it is over pressurised and that the sensor is working correctly. If so does anyone have ideas on why the pressure would have got so high in the first place?

Carrying on with this, could any one confirm to me that the high pressure switch is checking for too high a quantity of gas in the AC?

I'd agree with you, the car however has never been touched on the AC before now so don't see how it could have been overcharged. Faulty equipment is a possibility.

So it leads me on to think if i drop some of the pressure out by pushing on the centre pin in the valve it could work again. Anyone tried this? I looked at a pressure gauge you can buy, but that only connects onto the low pressure side, i guess this will equal out the high pressure side too. Does anyone know what the pressures are (high and low) to represent 500g of gas? I assume there must be a calculation for this, anyone?

Maybe i will be taking it back, i rang them a few days ago questioning the over filling but they said to me that it wouldn't make any difference but they'd do it if i wanted them to. I was questioning myself at the time but feel a bit more confident in what i'm saying now