At the beginning of each heating/cooling season, the system should be checked as follows:
To remove filter, loosen the thumb screws holding the filter panel in place. Slide filter out of the guides on either side of cabinet, insert new filter and replace panel. Some models come with a spacer so standard size filters can be used. Filters should be inspected monthly and must be replaced when dirty to ensure proper blower coil operation. See table 14 for replacement filter sizes or see the sticker located on the filter access door specifying the size of the standard throw-away filter which is used
B−Supply Air Blower
Outdoor piping insulation should be inspected yearly for deterioration. If necessary, replace with same materials.
Source: MaintainX (Community Member)