Unless otherwise specified, the goal of HVAC system cleaning is to restore the system to what minimum level of cleanliness?
Unless otherwise specified, the goal of HVAC system cleaning is to restore the system to what minimum level of cleanliness?
The minimum level of cleanliness for an HVAC system is that it should be visibly clean. This means there should be no visible dust, debris, or other contaminants. The other options specify more stringent or ambiguous conditions, but unless otherwise specified, 'visibly clean' is the standard goal.
Your answer is spelt wrong
The system is free not tree