I was experiencing the same phase when I first tried the ads1220.I suggest you go through the library carefully. I made duplicate begin functions for each channel by changing the configuration registers 0x91,0xA1. I'm able to read the data from other channels but the values are not accurate. I also observed that the ADC giving 40mv,33mv,25mv randoms when there are no inputs connected to the AN0, AN1, AN2. I connected pulldown resistor of 450Kohms, then the values showing are 0.18,0.9,0,1 mV etc., when no analog inputs are connected. I have been spending many hours but could not succeed from reading my 3 channel analog data from the sensor. 