I have had problems with the A/C on my 2004 Renault Laguna Sport Tourer intermittently not working over a period of time and sometimes emitting an audible whine when the engine revs go high on changing down gears. This whining noise can be replicated with the car sitting on the driveway with the A/C system on and increasing the engine revs. The A/C Doctor checked out the system and found it was short of gas. He evacuated, purged, pressure tested, refilled and tested the system and it has been working fine driving locally but on a recent long trip with the outside temperature reading 25 deg.C. it would not work at all above speeds of 40-50mph but still worked fine once I slowed down below 40mph again. I have spoken to the A/C Doctor again and he is baffled as he says speed should not affect the working of the system. I should be grateful for any advice you can offer.