I don't think A/C is really a good DIY project. Go to a independent auto A/C shop and explain the situation. Have them check the system for leaks and put back the correct amount of refrigerant and oil needed. Chances are they will do the test for free under those conditions since they wouldn't want to be responsible for putting in the wrong refrigerant.

You're in Palm Springs. That's no place to be fooling around without A/C.