Performed air duct cleaning and sanitation on the upstairs unit of 3 bedroom 2 system house. All upstairs vents and ductwork are clear of dust and debris at this time. Thermostat was up to temp when we arrived so the system was not on. Upon finishing the duct cleaning I turned the thermostat back on and the system is not starting. The house has been vacant for some time and the system has had recent work so the problem was pre existing. Customer is aware of the situation.Unable to perform duct cleaning on downstairs unit at this time due to construction still being in progress. Will need to return to complete the cleaning of the second system. Thank you for your business!