All of the o-rings, compressor, dryer, expansion valve, ac manifold seals, ac pressure switch were replaced and an ac flush was performed. The system was also vacuumed. I am just not sure if there is oil in the system.

I have 2 ports.

Is the port that is in the hose that is located higher in the car low pressure? How can you tell what is high and what is low pressure?

"Once you've added the refrigerant and the system is running under pressure, a standard check is to vent a little from the low pressure side and see that there is oil being carried through the system. Aftermarket oil almost always has UV-reactive dye in it, so it's a fluorescent yellow and very obvious."

If it was replaced with mineral oil, is there still a way to tell if the oil is present if it doesn't have dye in it?

Also, what is the best way to vent from the low-pressure port? Do you manually push the valve in while the system is running and keep a paper towel to collect any oil that may be pushed out?