GMC Troubleshooting Questions? Ask a Mechanic for Answers
How many days have you had the dye in the system?
Are you using a blacklight to look for the leak?
Does your envoy have rear AC and if so, have you traced the lines to it yet to try to find the leak?
Have you removed the blower motor to look for dye inside the housing or inspected the ac condensation for dye in it?