hi my air con on my 307 d turbo wasnt working so i took it down to a garage who did a leak test which came out ok and then filled the gas for the air con. but when it is switched on it doesnt seem to be working and just feels the same as having it on 14 eco. sometimes when the climate is switched on it doesnt work straight away and makes like a whirring sound as though something is blocking it. any suggestions as to what this is and what the problem with the ac could be? also does anyone know what a cabin filter is ?