AC Recharge

[TexasTom]

Dash air has not been very cold for a while so I got a can of the AC Pro refrigerant with the gauge and added 32oz. (I know the proper way is to have a qualified AC tech service the system, but I wanted to give this a try first)

So the gauge still shows the refrigerant level being low, but I get 45 degree air when it's 75 degrees outside.

So do I call it good or should I add some more refrigerant?

[Spk64]

30 degree differential is pretty good. Too much and performance will drop

[BFlinn181]

If you've got a 30º drop from ambient air to vent temperature, I'd leave it alone. It would be a good idea to have a full manifold set of gauges to monitor high and low side pressures before adding more. R-134a refrigerant isn't as good as the old R-12 and can lose efficiency with too high a pressure as well as with too low. https://www.ohio.edu/mechanical/ther..._tables/R134a/

[Old Scout]

....you are pretty much flying blind without gauges unless you know the capacity of your system and start from an evacuated state. Sounds like you probably have a small leak so you will be back here again--adding 134a. A 48 oz system seems to be fairly common size so 32 oz probably got you back to the lower end of the operating limit--so good enough for now.
PS--think the theoretical limit for the cooling differential is 22-25 degrees. The mix of air being drawn thru the evap coil determines the ambient temp from which you measure differential. So if you start at 90 degrees in your vehicle, you can expect conditioned air to be around 65-70 degrees. As the air cools in your vehicle, say 70 degrees, you should then expect 45-50 degree air from vents, and so on. This differential also dependent on how efficiently your condensing coil is being cooled by air flow.