Though your comment says "4 channels select", you have only enabled 2 (AN0 and AN1)
I also seem to remember reading (someplace) that you have to disable the ADC to change any configuration parameter. I can't find the reference but I do it, it works, so it can't hurt.
Your code should be:
Code:
ADCON0bits.ADON = 0; // Disable to change channel
ADCON0bits.CHS3 = 0;
ADCON0bits.CHS2 = 0;
ADCON0bits.CHS1 = 0;
ADCON0bits.CHS0 = por; // Por = 0 for AN0, Por = 1 for AN1
ADCON0bits.ADON = 1; // Enable