
If you are sure that the ad said Air con then speak to them about it. It will be a case of how you handle them I guess , They are not legally obligated to give you any compensation ( unless you can prove that the ad did exist and that it affects the value of the car by a huge or reasonable amount) They would have been obligated to give you your deposit back and set you free from you obligation to buy the car if you noticed between leaving the deposit and actually paying the final amount and collecting seeing as the Air con was material in your decision to buy the car. If you can prove the ad was as you say you may have a case for them taking the car back from you. Compensation is always a toughy as the amounts are measured in how much you have actually lost , they may argue you have not lost anything in monetary terms.
Dealers or at least some need the sales so badly they may could offer you some extras as a goodwill gesture.
The problem always lies with proving you have been misled afterwards. Could you not find out from the advertising site when they changed the ad if they can tell when it was changed you would at least have some bargaining power. Thing is what the law says and how it is implimented is TWO very different things. People are stung everyday as it is so hard to do anything about it.
Probably went round in circles a bit here but my point is really to speak to them and see if you can get a freindly resolution you may want they to help you out in the future with car trouble so best to stay on their side.
BFN Pam