How to investigate a problem with blown 50 amp HVAC fuse without power?
The next step is to see where the short is, and for that you will need to check the resistance of the compressor and fan motors. The exact wiring can vary by model, but basically, you need to check the resistance between the wires going to each motor and see if any are shorted. 

As a first step, you can probably just check all the wires going to each motor and see if they are shorted to the case of the motor. If a wire breaks internally it can ground out to the motor housing. Beyond that, you need to understand more how the motors are wired.