Norcold 4150 three way not working in 12 volts

Thanks for all of the helpful information, however I tried cooling it down with 110v. started engine, selected battery power and error 6 displayed. Error 6 indicates no 12 volts, however I measured 12.5 volts at connector to fridge.:h

The 12 volt section of your 3 way is a MAINTAINER of existing interior temps. It is NOT designed to cool the refer DOWN to operating temps. So, if you have the refer at operating temp, then you MUST have the engine running to run the 12 volt heat element to MAINTAIN the existing temp in the refer. 12 volt 3 way refers must have the engine running to function on 12 volts. You must use 120 or LP to get the refer to operating temps. Doug

the manual says

Push the source button several times, as illustrated. Push until the desired source
(A, ‘auto’) is selected and displayed.
If the engine is running, DC mode will be selected and displayed.
If the engine is not running, and 120 volts AC is available to the refrigerator, AC mode will be
selected and displayed.
If the engine is not running, and 120 volts AC is NOT available to the refrigerator, gas mode
will be selected and displayed

the manual says

These models have 2 connection points to prevent the battery from being discharged by the
refrigerator when the engine is not running

there is a connection on the back that senses the engine running the manual shows

D+ signal orange wire, + when engine runs

the current draw when running on 12v is above 17 amps

Does it actually run with the engine running?