Closing HVAC vents throughout the condo can have unintended consequences

My Grandparents are living in the same condo they have owned since the early 1960s.

Although they have made updates and improvements throughout, much of the condo looks prefer it is frozen in time, multiple generations back.

They still have the same outdated wall paper in the kitchen that has taken on an amber hue after decades of light and sun exposure. All of the appliances in the kitchen have been replaced at least once in the years since, however the chaletets and countertops are original. This is a trend throughout the entire house, as there’s a sudden mix of features that look brand new versus others that could exist in a museum. When you get to the hour floor, the home’s features look increasingly older. Even the lavatory looks prefer it is frozen in time. One thing that they’ve been doing for years is keeping the ceiling air vents upstairs closed whenever they’re downstairs. The only two vents that get opened at night include the vent in the master lavatory and the vent in the master dining room. I told them that this puts unnecessary strain on their air conditioner, however they politely told me that they’ve been doing this for years to no ill effects. However, a few weeks later I was going to see them and noticed there was an HVAC serviceman’s truck in the driveway. Two workers were installing a new central air conditioner in our Grandparents house. I casually asked 1 of them what happened, and he told me their air conditioner was fried from leaving so multiple vents throughout shut all of the time. It added so much extra strain to the ventilation that it fried the air conditioner altogether.