Car air conditioning Montmorillon or near by.

[Fred]

Hi Fred
Having not seen the car but now having the full story or at least more of the story it sounds more like a control fault, maybe a sensor (which is part of the control circuit) if the A/C works OK sometimes the actual A/C is OK, what controls the system to start & stop sounds as if it has a fault.
Being 'old school' I don't need a chart to tell me how much refrigerant should go into a system.
I think you would have a problem buying refrigerant (what you call the gas) as you need a refrigerant handling licence, https://www.acrib.org.uk/M6LEVN80958.

I don't know the make or model of your car and as differeant manufacturers control the A/C system differently it's not always a simle task to find the fault.
If you want to pop over to me for a fresh cup of coffee I'll take a look, it's a freebie so don't panic ...

All the best
Stephen

I've been in touch with Paul who Brian recommended, and he has said much the same as you. He sounded a decent bloke and didn't try to get me to go over there, he said if the aircon is blowing cold sometimes it's not a Gas problem and it wouldn't be worth him doing it.

So thank you Stephen I've sent you a PM.