You didn't mention you were taking it to the dealer. A simple $7 can of refrigerant could have solved your problem, and you probably wouldn't have needed a whole can. I too would tend to argue against the bogus diagnostic fee, since they did something you didn't ask of them, but it's gonna be a tough one. Were your instructions in writing? Once the techs spend time even just looking at a car, they will feel they need to be reimbursed which is understandable.

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