Also, some units will have a system of monitoring the
humidity level in the air and only humidifying when
necessary to ensure that there is not too much moisture in the air and that the unit does not use more energy than
necessary.
After having the shop that repaired my R12 AC system last year mildly to moderately under - fill it (before it was ice - cold; now it cuts the
humidity ok but only gets cool only after 10 - 20 minutes of highway driving) I got the
necessary certification and am planning to top the system off to get it up to the
level it should have been filled to.