my son is 12 and he does not want to see his dad on his weeekends

Your 12 year old son does not have the authority to override a judge's order.  You, not he, will be held in contempt of court, and punished, if your son's father is denied his visitation rights.  If your son does not want to go visit his father, the appropriate thing to do would be to first inquire of him as to his reasons for not wanting to go, and then to file a motion for modification in court.  Then you can present your case to the court, and give the Court the opportunity to modify the order if it agrees that your reasons and those of your son constitute a substantial change of circumstances.