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Hello, Code 178, Indoor Units printed circuit board, or 24 volt control circuit is non functional.. it could be a bad thermostat, printed circuit board, or just an oxidized wire connection. Trouble shooting that is difficult. Many if not most HVAC technicians will resort to inspecting those components for burn marks or bad connections and replace the most suspect piece or pieces and hope for the best.
Tell me a lot about your technical skills in electronics so that I can coach you most effectively, or if none of this is in your bag of skills, tell me which direction you are from the center of the nearest city so I can look for a well rated company that has skill sets in range.
We can go from there