At 09:21 PM 9/4/2012, tom ring wrote:
>My fridge works fine on 120 and propane but poorly on 12 volts.  I
>have checked
>and it draws 6.3 amps on "12" volts which seems to be as expected.

Check along the 12 V wiring for voltage drops.  Replace fuse on
pillar with a Littelfuse glass version that isn't prone to losing
contact at the retaining hole as the Euro fuses do.  Increase spring
tension there.

Check using an inverter to power it on 110 V while you're driving
down the road.  The fridge never works as well when under way as the
vehicle's motion interferes to some extent with the internal
flows.  If no inverter, use propane.  If you stick a thermometer on
the cooling fins/tube with heat sink compound and cover it with putty
you'll be able to see fin temperature rise within moments of driving off.

Check supply voltage at load end of fuse and current (ammeter
inserted in line with fuse -- I think the supply wires on that
fixture use screw terminals).  Leave the fuse in circuit since by its
nature it produces a voltage drop.  Product of voltage and amperage
should be at least 85 watts (rating of the heater).  If not there's a
poor connection somewhere and/or thicker wires needed.  Poor
connection may be on top of the fridge.

If above checks are ok, pull fridge and investigate the heater pocket
- heater is held in with a setscrew.  Rarely they break off the
boiler, otherwise it's possible that corrosion may be interfering
with heat transfer (not too likely given that the identical AC setup seems ok).

The easiest overall solution *may* be to simply use an inverter on
the road.  This minimizes voltage drops (taken as percentage of the
total) and lets you have a thermostat without modifying the fridge.

Yours,
David