Car: 2007 Type R GT FN2, Red
Join Date: 21st July 2019
Location: Devon, UK
Thanked 3 Times in 1 Post
All good advice above, especially from Jon-G but I have a few things to add.
Legal Stuff, Oh I know what you're thinking but as I am licenced by DEFRA to work on automotive air con systems I have to take note of it!
If any system I work on has less than 50% of it's normal charge (by weight) of gas in it then before recharging I must pressure test the system using Oxygen-free Nitrogen at 150psi. It must hold that pressure without change for at least half an hour before I can consider it to be leak free. BUT, sometimes, not often but sometimes, a leak can be so tiny it won't show up which is when the dye in the refrigerant part comes in.
In general at 150psi you can hear a leak and track it down that way, with a stethoscope. But despite the legal aspect if you have a leak then there is no point just recharging it anyway because you'll be back to square one in a week or so.
All the other comments are correct. No gas pressure and there is a sensor which will stop the compressor running. That's to save the compressor from running unlubricated, don't forget there is oil in the system as well as gas which can/will leak out!
Condensers are the commonest source of leaks because they are in such a vulnerable position, they have to be to get the airflow through them. But there are other possible places so don't change a condenser, or anything for that matter, without proof it's leaking.