Dangousity

Issue 1: The Ac seemed low on 134a today, so I went and bought a can of refresh at the local auto zone and put it in. Drove home, came out later and drove into town. With the Ac on it seems to be engaged and quickly clicking off, then repeating this process every 2-3 seconds. Is it possible the system is over charged? Should I evac the system and get it recharged again?

Issue 2: My radiator fan does not turn on until a little over 3/4 of the way up on the temp sensor. I feel this is TOO hot, Any good way to test the water temp other then putting a thermostat in the coolant?