You know the test... pump system down, disconnect compressor leads, power up the condenser fan and let it run until discharge air is same temp as entering air. Do a pressure/temperature comparison and if pressure is higher than the P/T chart says it should be, you have noncondensables.
My question is, do you have to do the pump down? Not all condensing units have the internal access fitting, making it difficult and time consuming to perform this simple test. Can the test be done with refrigerant equalized throughout the entire system?