How to display potentiometer value from dspic33 microcontroller
You are not waiting for conversion to complete. 

Algorithm for ADC operations is as follows:


Initialize ADC and Pin for Analog channel
Start the conversion
Wait for conversion to complete
Read the result buffer when conversion is complete
Go to step 3


In your case, you are not waiting or reading the result buffer.
Datasheet is helpful enough to understand the registers.