Schematic shows 10k series sensor (also 10k in a specific environment). Point AC is connected to this voltage divider.
If the comparator isnt blown, its input impedance is very high -> shouldn't affect voltage.
..nor will the capacitor affect voltage.
Connect AC to an analog input - read it with analogRead - print result.
If u get 1023, the circuit isnt as described or a component is malfuntioning.