Isotherm DR160 dual voltage issue

[Tracyandkimo]

We have a freezer over freezer Isotherm DR160 that runs on either 12 or120. It prioritizes 120v when it has both, but should switch to 12v automatically when 120v is not available. It does not. Voltage is good. Checked it under load. It reads above the 11.8v that the control unit looks for to start. Replaced control unit last year for same reason - $400+. I don’t feel this should be a yearly thing. There used to be company, Isotherm-parts.com, that sold parts and offered technical support including trouble shooting guides. For some reason they’re no longer affiliated w Isotherm and their site says to contact Isotherm for info., a parent company manufacturer that offers no support.
Anyone w suggestions about the unit itself or info on who might help, would be appreciated.

[wholybee]

FWIW, I have recently dealt with Isotherm directly for support and they were responsive and helpful. I just emailed them at info@iwmarine.com. 11.8V seems very low. Not sure it that is part of the problem, but I would definitely work to get that up. How did you measure that under load if the unit won't start?

https://www.indelwebastomarine.com/us/

[Tracyandkimo]

Thanks, I’ll try that email.
11.8v per the tech from Isotherm Parts, is the minimum the controller needs to see. Apparently it looks three times and not if seen, it stops trying. It has 12+v. I wasn’t accurate when I said “under load”. I checked it as I turned off 120v supply. IMO if the controller had switched to 12v, I would see a fluctuation as the compressor/fan started. No fluctuation so I assume it’s not switching as opposed to it switching, the components having the 12v, but not starting.