freon leak on 2004 GMC Sierra 1500

we check under the hood and no leak, where and what would be the cost.

Asked by for the 2004 GMC Sierra 1500
Cost would depend on locating the leak, evacuating the system and then recharging the system.Cost ill certainly depending on what is found to be wrong.
I was told by a freind that it could be in the dash, if true how long would it take and about the cost.