From the look of it, someone has done a (marginal) retro-fit to R134a. They only put a fitting on the low-side service port, so that shiny fitting without a cap is where the R134a goes in. It would be nice to have an R134a fitting on the high-side so you could see what the pressures are. If it's empty, you'd want to pull a vacuum on the system to remove any air/moisture. Capacity of R134a if empty is +/- 20 ozs. Hope it has the correct oil (PAG 46) instilled.