R134a was used.
Today's temperature when I was doing this was about 73 or 74F with a relative humidity of between 40-50%. The pressures read 35 Low & 150 High; with a center vent temperature of about 45. I added just a little bit more (that's a scientific measurement
) and called it good. The 40.7F reading was with the hood open and the engine throttled up a little bit, but certainly not highway speed. All center vent readings were with the fan speed on low.
During my test drive, the low center vent temperature I saw was 44.4F and highs of 49.8F; possibly due to different engine speeds, travel speeds, time stopped at red lights, etc.
Hopefully when it gets back to 95F the temperature will be under 60F at the center vent. I have asked the owner to give us an update when the heat returns.