Had my 12 plate fiesta Zetec 1.25 for nearly 3 months now with just over 2500 miles on the clock. Now with the 29 degree whether here in good old Hampshire, I have been driving with the air con on. When I first turn it on the car jerks which is understandable as i can imagine it uses a lot of power to get it going. However, every now and then the car will jerk a couple of times and then carry on as normal. Their is a noticeable difference in how the car drives with and without the air con on. Is it normal for it to jerk like this ?