How much does a car A/C in a perfect order leak?

I hear some people say that refrigerant does not escape as long as there is no "leaks" but I don't think there is such a thing as a leak free open-drive refrigeration system.

What is a range of annual refrigerant loss rate in a modern A/C system in a perfect maintenance?

zero, if the seals dont leak and you dont have any other leaks then you will not have any loss of refrigerant, "no "leaks"" being the key phrase here.

Hi pwned, as dane says the target is for zero loss though eventually compressor shaft seal and "o" rings will give trouble.

Maybe things have changed, but I thought the hoses used in auto AC had a small leak rate. Maybe they have changed the material.
My car is a 2001 I bought new and it has never been recharged.

Car ACs looses refrigerant all the time.
This due to "diffussion" through the flexiable hoses. The lose is calcualted by temp, pressure, refrigerant, area and the type of hose.
but in real terms is very minor.

doesnt hurt to flick the old ac button on every week or so during winter for a few minutes to help keep the orings and seals lubed up!

All elastomers are permeable to some extent, they let refrigerant out and moisture in (at a very slow rate) that includes all hoses and oring seals.

The biggest single leak path in an automotive open system is the compressor shaft seal which could be a carbon face mechanical seal or lip seal depending on the compressor.

The typical hoses we use have an effusion rate of 2.4kg/sq.m/yr

I still see r12 systems from late 80s and early 90s running cool and never recharged, not many though.

New cars use barrier hose that has a nylon liner because the smaller molcule size of 134a will leak at unacceptable rate through rubber hose.

There are a lot of converted systems around and they leek very small amounts through there r12 type rubber hoses due to fact they are oil ladden and this pluggs the holes in the rubber, sort of a mineral oil barrier.

EC Directive 2006/40/EC states for a system using a refrigerant with a global warming potential of 150 or higher (eg R134A) the maximum leakage rates are 40grammes per year for single evaporator and 60 g/yr for dual evaporator.

Does anybody know who is responsible for this? service tech? manufacturer? distributor? service company management? car owner? car driver?

2006/40/EC only relates to MAC systems for new cars, and therefore the responsible ones are the manufacturers.