Who is responsible for electrical, plumbing and air conditioning?

Is the electrical, plumbing, heat, and AC that is under or outside the homeowners' responsibility or the associations? We are a small condo association with only 6 units. All units have their own entrance, similar to a townhouse structure. All condos are connected to the same heat and water source and it is paid for by the association. Although each unit has a separate thermostat and vales for their heating . We have a crawl space below with electrical and plumbing. One of the valves for one of the units needed to be replaced. There is nothing in the Declaration to specify whose responsibility it is.  North Dakota