The gauge set does have a yellow line but I didn't realize that was what it was for. Good to know for future reference.

I did feed the gauges up to the windshield but the angle makes it very hard to read them accurately.

I will add measuring the duct outlet temperature to the list of to-do items.

I anticipate that if there is an external system leak that it will result in the A/C not working due to low refrigerant level with the amount of time until that happens related to the size of the leak.

 

1 have a 95 SC2 that runs at about 175/30 and will last for 3-4 mo on a slight overcharge until it leaks out. Of course every system holds a different amount, the compressors are different, blah blah blah -- my point being I would expect you get into the fall with it. If it was a massively large leak, you likely would not be functioning at the level you are.
Also: Check the lo and hi side ports for leaks.
They usually don't get used much during the life of the vehicle, but when you start connecting and disconnecting gauges in year 20, they don't always seal properly. The end result is a recharged system that may leak more from the ports than it did from the original leak. adding more confusion to the mix.

Spit (excuse me, saliva) seems to be an ideal test fluid for leak detection at the ports. Transfer some saliva into the ports and look for bubbles. If you have a leak on the high port, you'll usually hear it and refrigerant will disappear.

They make different "re-coring" kits to replace the inner valve and seal. Some claim to be able to do it with the system still charged.

I've no personal experience on this one -- other than having someone else recore several of the valves on my SC2.