Thermostat blank on arrival. Found limited voltage at thermostat. Traced high voltage circuit for AHU until finding voltage break at AHU disconnect in attic. Aged Square D disconnect box is losing 240v across breaker. Discussed replacement of disconnect as well as need to perform wider electrical inspection. Recommended enrollment in maintenance plan to ensure home systems regularly inspected. Client accepted recommendations. Balance for project collected. Please schedule electrical technician to replace breaker as well as inspect broader home electrical systems.