I have an ac question on my gmc sierra. I was wondering if a vac can be pulled on a charged system without loosing the refrigerant? I replaced a failed line and pulled a vacuum for and hour, charged it with dye and ran the ac for about 10 miles. No leaks. But i dont think the vac pull was enough. Now i want to pull another vac for longer issuring as much contaminants are removed as possible. Thanks for the input.