Hello, my name is ***** ***** I will try help you with this.
It is possible for gas to escape over a period of time without there actually being a fault in the system.
The AC system should be serviced every year.
It should also be used on a regular basis including during winter time.
The reason for this is the gas also contains a little oil and this oil lubricates the seals in the system. If the AC is not used often or is not serviced regularly then the seals can dry out and shrink a little. This is what causes the leaks.
When the system is then regassed, oil is also added and this rejuvenates the seals and the system doesn't leak.
Most people don't service the AC system because they think if it aint broke, don't fix it.
They only do it once it doesn't work. I suspect this is also what you do.
You also need to use it more during winter time. The AC is not only for cooling the air, it also dries it by removing moisture from inside the vehicle.
I hope this explanation helps you understand why there could be no gas in the system but also no leaks to be found once it has been regassed.
OK Mark, but (1) car was (allegedly) re-gassed at the end of April, just after I got it. That didn't restore proper a/c. (2) Your assumptions about my use of a/c are unwarranted. I have it switched on all the time and have done for very many years. (3) I have a particular regard to a/c as on my 1998 323 all the major components failed one by one, at the same era of age, fairly costly to deal with, but the result is superb a/c. I admit even the fairly knowledgeable but determined enthusiast like me could be deceived, but failure of components is natural with age and use (I've heard plenty of stories of failed compressors at 50K or less), and I still suspect Max my 650 has still not ben fully diagnosed (he is now 8 years old, 81k, currently undergoing a Reburbishment and Preventative Maintenance scheme -- we're not finding all that much that's "wrong"). Many thanks for your help. Regards, David H.