The reason for that, the drop in temperature of air after the usage of cold air intake system is small which hardly boosts up any performance. (motorbeam.com)
Ensure that all supply and return vents aren't blocked or closed, as this causes the return duct to pull in cold air from cracks in windows and doors. (rismedia.com)
Those outside units would be blowing very cold air in the winter and warm / hot air in the summer yet the graph shows steady winter and summer warming from 60's onwards. (wattsupwiththat.com)