The place to start is with careful voltage measurements. The fridge can
be set inside the van and operated with the wiring hooked up and no
propane connection.  The 12 volt heating element has 2 wire leads that
are screwed to a terminal block on top of the fridge. Remove the metal
cover over the block. Identify the 2 wires and measure the voltage
between them on the element side of the terminal block when the fridge
is set to 12 volt mode and the engine is running with the dash alt/bat
led off. Write that voltage down. Then leave 1 probe on the + wire and
move the other probe to clean bare metal on the van body. Write that
voltage down. Now, with everything still running the same way measure
the voltage on the main battery posts, write that down.

Now turn the headlights on low beams and the dash fan on speed 2. Do all
the above measurements again and record them.

Comparing the measurements will give you an idea of where the particular
weak spots are for your fridge 12 volt operation.

An aux battery can actually make things worse for the fridge, depending
on how the aux battery is set up. The typical GoWesty aux battery
charging arrangement is just about worst case.

Mark

Jeffrey Lee wrote:
> Mark wrote:
> "The 12 volt mode operation often has degraded due to aging of the wiring
> connections. This can be remedied. Also the cooling on 12 volts can be
> improved by a change in the path of the power supply wire."
>
> Mark, interested to know more about this. I just pulled my fridge for it's
> somewhat overdue quarter-century overhaul, and would like to know what
> wiring should be upgraded/replaced to boost 12V performance.
>
> FWIW, I'm running on a relay-isolated AUX battery, if that matters. My
> Dometic has always performed pretty well on all modes, though as you say,
> 12V power is more of a 'maintenance mode' ...
>
> Thanks!
>