Car has been working fine for the last 3 years (since I owned it) and due to the heat where we live its on all the time.
If you are driving along it is fine and cool, So we know it has gas & have been told today by an air con tech that it is still full.
However if you stop for a few minutes you will then hear the fan cut out and then almost straight away the air con completely stops and we are flooded with warm air.
It does appear that if I rev the car it then works.

Any ideas and why does the fan stop working?

Thanks in advance.