An unbalanced HVAC system...
...will present visible clues within the space such as: condensate on diffusers or wet ceiling tiles (insufficient velocity), room too cold or too hot (failed damper actuator), exterior doors hard to open (negatively pressurized), odorous restrooms (neutral to positive pressure), visible cloud above your head (blown charge of R22 or the like), etc. etc. Something tips people off to the problem. But what would tip you off to the presence of Covid 19 ? Only Blocloud can do that!