When, say, your internet craps out, would you rather your ISP try to resolve the problem, or schedule to send a tech out to your home before they start working on fixing the issue?

Groceries see HVAC in the same way. If they can get their issue addressed or diagnosed by their HVAC contractor without him having to schedule and physically travel to their site, they'd prefer him to solve/start solving the problem immediately. Time is money and the faster the tech can diagnose the problem, the faster he can get on fixing it.

And yes, the prevalence of these systems means that many HVAC techs have the ability to turn off their customers' air conditioners/fridges. They don't use it maliciously, because that would be actual suicide for their business.

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Source: A close friend of mine runs an HVAC business (~8 employees) doing residential and commercial installs, repairs, and maintenance.