Does any one know how to test an air conditioner for freezing?

Look at the evaporator inside of the indoor unit. Is it clear, frosted or iced? Many times the copper lines will be frosted or iced.

If you are talking about freezing the evaporator coil , you have to open up the coil case and look at it, if it is frozen you will see it. If the suction line is iced up then that's a good indicator.