Having not used my aircon for a while on my '07 1.9JTD I have a fault ... surprise!! Aircon blows cold air ok but it is making the engine surge, effectively slowing and speeding the car up as I go along, making a low drowning sound as it cycles. Multiecuscan doesn't give me any parameter details for it ... Latency too high. I thought it may be the aircon clutch slipping but am convinced it is something else now .... pressure switch? Can anyone throw any light on it for me?