If your AC is the type that vents out indoor air then this makes sense (though smaller AC units tend to just circulate the indoor air after cooling/dehydrating)

If your AC is the type that vents out indoor air then this makes sense (though smaller AC units tend to just circulate the indoor air after cooling/dehydrating). Depending on the sensor technology in your CO2 meter, it could be sensitive to temperature, so that may be worth trying to exclude as a factor.