Cult logic

The AC on my Swift wasn’t great.
I recharged it as the pressure was low but not empty - so hopefully not leaking.
Now gives out a nice 8 degrees when driving but goes up to 15 when stationary.
Could be the compressor is on the way out so not working well at tickover - or lack of airflow through condenser. Or something else…
That’s my logic anyway.
I suppose the next thing to do is coast down a hill in neutral and see if the temp rises.