Well, the way it works in practice is that most buildings have a multi-year service agreement with either the service arm of a major manufacturer, or a third-pa

Well, the way it works in practice is that most buildings have a multi-year service agreement with either the service arm of a major manufacturer, or a third-party maintenance firm. A really large property complex would probably have a mechanic who essentially is full time at that complex. But as a practical matter, you need access to spare parts, drawings, etc, so it is hard to be a one-man show. Because of parts access and licensing, I think it would be impractical for most commercial landlords to keep a mechanic on staff. Usually for any building there is a primary mechanic who is assigned to that site, so that he has familiarity with the quirks of the system, relationships with the landlord's staff, etc. Of course mechanics in the same office cover for and assist each other.