In Reply to: cab air cleaner posted by Holland Land Co. on February 22, 2009 at 11:04:32:

Change it once a year and never touch it otherwise. I know it gets really nasty dirty, but it never causes a problem. It doesn't flow that much air as you think, as it is just the filter for the pressurizer fan.

Also make sure your right side rotor door is sealed up good, as in good latches or foam seal strips.