Toyota Repair: AC Pressures and ambient temps, ambient temp, autoparts store

Question
I am going to add Freon to my 2000 Toyota and need your expert advice. I am only going to use the low gauge for pressure reading when filling.

I understand the gauge has pressure and temp readings but I am unsure how to coincide the ambient temp with gauge pressures. I believe the gauge temp refers to the temp of the Freon in the system and not the ambient temp. Do the charts have ambient temps that coincide with pressure readings? Could you help me with this?

Here's an example:

Let's assume the ambient temp is 80 degrees. How would I determine the correct pressure reading based on this using 134a? Can you direct me to a chart that has these readings?

Also, if the freon is so low the compressor isn't running, can freon be added without it be running? If not, how is this done?

Thank you very much.

Answer
On the R134 system the freon is added with the engine not running, ambient temperature is irrelevant as far as low pressure is concerned, the low pressure should always be between about 30-47 psi for the system to cool properly. The recharge kit from the autoparts store usually comes with instructions and has a gauge on it.