The A.O. Smith Voltex series of heat pump water heaters are using a CTA-2045 interface. The CTA-2045 specifications are available for free and contain pinouts and protocol information. It's a RS-485 bus. It uses an AC UCM connector, also carries AC (110V?220V?)? Please send me part numbers if you find out.
This is true for the HPTU-80CTA, HPTU-66CTA and the HPTU-50CTA
This instructable is modifying an IRIS system.