Diagnosing a vehicle's ac system is not a simple process.  Temperature cause's expansion and contraction on the metal's and rubber that the system is made of. Hence if you have a leak it could seal itself when these temperatures change from operating and the vehicle needs to cool to reveal leaks. So the days of "Can you look at my AC real quick?" are no more. especially with costs of parts and chemical these days. Allowing time for diagnostics is critical for proper estimate.   

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