If the HVAC system

If the HVAC system discharges visible particulate into
the occupied space, or a contribution of airborne
particles from the HVAC system into the indoor ambient
air is confirmed, then cleaning is highly recommended.
See the guideline to this standard for discussion of the
Particle Profiling (PP) procedure, which may be used to
confirm if non-visible contaminants are being introduced
into the indoor environment via the HVAC system.
3.5.2 Compromised Performance
Cleaning is highly recommended for heat exchange
coils, cooling coils, air flow control devices, filtration
devices, and air-handling equipment determined to have
restrictions, blockages, or contamination deposits that
may cause system performance inefficiencies, air flow
degradation, or that may significantly affect the design
intent of the HVAC system.
3.5.3 Indoor Air Quality Management
Indoor air quality management plans that include
periodic cleaning and maintenance are highly
recommended to minimize recurring contamination
within HVAC systems. It is highly recommended that
special consideration be given to buildings or residences
with sensitive populations such as individuals with
compromised immune systems, and specialized
environments or buildings with sensitive building
contents or critical processes.