You are going to need a properly functioning TXV in order to run the system long enough to check for the proper charge. Your best bet is to pull the charge R22, replace the TXV then leak test the system with dry nitrogen. If no leaks are found then pull a deep vacuum on the system. After you pulled a vacuum you can add the R22, there should be nameplate on the unit showing the lbs and oz the system holds.

You can weigh it in ( special tools required) or slowly add it in through the gauge set. If you are unfamiliar with this you can contaminate the system with non condensable gas(air), and then you need to start all over again.

You need to make sure your pressure temperature relationship is correct and not over charge the system. Overcharged = slugged compressor = game over broken compressor!