Hopeful high school graduates aren’t the only ones trying to get into Harvard. Getting on the university’s list of approved vendors can be a boon to any commercial contractor, but few make the cut. For Aspen Air Duct Cleaning, it started with a call from a mechanical contractor working on the university’s renovation of its Girguis Lab. Engineers had just installed a new 8,500 CFM air handling unit that was meant to supply heat to the lab and an adjacent facility. When the unit was brought online, however, its fan was operating at around 97% of capacity with little effect.