Chef,
you need to go to your nearest a/c shop and connect your system to their Gas Analyzer. That's the way to tell what is in there, unless a reputable shop placed a sticker in the engine compartment which gives the information.
If you have R134a gas, don't expect a lot of cold air, especially during idling. Once the car is moving, then it gets cool. R134a sucks.
There are better alternative refrigerants you can convert to, but it requires
a knowledgeable and certified a/c tech to convert. A/C is not a do-it-yourself job, especially the Jaguar Delanair III system in your car. Refrigerant can make you blind. The system needs to be evacuated if not flushed to do a conversion. Bite the bullet and do it right. Wait until early Winter when shops are not busy and the price is better.
Ex