Fridge Mods

First the Refrigerator Door

Two members of TheSamba.com mailing list (MootPoint of New Mexico and Corn1849 of Idaho), noted that it would be a good idea to cut the top off the fridge door to prevent the cold escaping while lighting the propane. MootPoint commented on his mod that the cut was just a little too close to the air pump knob, making priming the fridge difficult. Corn1849 decided to leave the top piece off the door altogether. So I tackled the project, with a couple of changes.

Click on the image to see it full size.

The rough cut.

To make working on the door easier, it was dismantled completely. A cut-line was drawn just above the rubber seal, just below the information plate.

The cut was made to the shape shown, using a bandsdaw with fine blade. Taping the face of the door also prevented chipping of the surface. The right side of the door (bottom here) is cut higher to clear the hinge, and the other side is cut to match.

Plenty of room to get at the controls.

A 1/2" wide brass piano hinge was fitted between the top and main section of the door. A recess was routed in the two edges to allow the piano hinge to be sunk by half its thickness on each piece. This meant the curved cuts at the left and right ends match with only a very small gap.

Without letting the cold out of the fridge, all the controls are easily operated. On the left side a 1/4" rare earth magnet is just visible, set into the edge of the door. A mating magnet is also set into the upper part so the two attract when the top is closed.

The operation warning plate was screwed back to its original location. However, now it appears it should be turned over so I can read it while operating the controls!

All sealed up.

The rare earth magnets hold the top portion of the door upright. It stays closed even on rough roads.

Now the Cooling Fans

The original circuit of the Dometic fridge.

Power from T3a/1 is continuous 12V and comes from the 8A fuse behind the driver's seat.

Power from T3a/3 is switched on by a relay under the dash only when the vehicle is running and comes via the 16A fuse behind the driver's seat. This powers the 12V heating element.

T3a/2 is the common ground for the 12V circuits.

The object marked oC is the thermo-switch mounted to the exchanger coils at the back of the fridge and closes when the fins reach a high enough temperature, thereby starting the fan motor from the continuous 12V supply. This is the reason the fan can run even with the vehicle switched off and the fridge switched off or to propane.

The SWITCH selects either 12V or 120 volt to the respective heating coils.

T'STAT, the thermostat, controls only the 120 volt element and propane valve. The 12V heater is not controlled by the thermostat.

The printed circuit board to control the two fans and indicator LEDs.

A small piece of 'breadboarding' PCB was laid out with the components to

  • limit the voltage to 9V
  • switch either the interior fan on or the interior and exterior fans on, or both fans off
  • provide LED indication of the selected fan or fans
  • prevent the vehicle's 12 volts from damaging the circuitry when the fridge heat exchanger fin thermoswitch cuts in.
It was felt that 9V was sufficient under normal conditions for both fans, but if the fridge thermostat called for the external fan to run, it will still operate at normal 12V no matter whether the fan was switched on or off.

The additional circuit for fans and LEDs.

The only modification to the original Dometic wiring is the soldering of a yellow lead to the thermoswitch (oC).
The yellow and blue wires simply connect to the terminal block screws.

Continuous 12V from T3a/1 is reduced to 9V by IC1, a 9 volt regulator in a TO-220 case capable of handling 1 Amp.

SWITCH is a double pole 3 position (on-off-on) which sends the 9V to either:

  • D1 and to the external fan, R1 and LED1 or
  • D1, the external fan, R1, LED1 as well as R2, LED2 and the internal fan (marked M) or
  • in the central position selects neither fan.
D1 is to prevent the vehicle's 12 volts from affecting IC1. It allows the external fan to run slower (on 9V) when selected, but also allows it to run at full speed on 12V if thermoswitch (oC) cuts in.

R1 and R2 are 5.8Kohm resistors to limit current to the small LEDS. They prevent the LEDS from being too bright and burning out.

LED1 and LED2 are very small green low power LEDs.

Interior fan running.

The switch up activates the interior fan and the top LED only.

A hole was drilled in the plastic fascia just large enough to thread the switch into, but not through. The lock nut is behind the fascia.

Interior and exterior fan running.

The switch down activates both fans and both LEDs.

Two holes were drilled just large enough to press the LEDs into.

Note that the instruction plate is now the right way up when the top of the door is folded down!

Interior fan above the cooling coils.

The subminiature fan was mounted in a plastic frame and held to the roof of the fridge with hook & loop tape. It does not touch the cooling fins. Two reasons for this:

  • Hoping to prevent resonating noises from the fan being amplified through the body of the fridge - it seems to work.
  • Easy removal of the fan if (when) it fails, or a different size fan is needed.
There is a plug and socket in the wiring so that the fan can be disconnected without desoldering or removing wire through the fridge case.

Exterior fan below the exchanger coils.

The miniature fan was mounted in an aluminum frame and screwed to the back of the fridge. It replaces the original Dometic fan.
The bottom of the mount is open to allow natural air circulation when the fan is off.

The upper part of the shroud is held to the exchanger fins with a J bolt.

Minor Mods to the Dometic

The priming pump and ignitor.

The non-return valve in the air line (top right) had been stuck closed for years so no amount of pumping was forcing air into the combustion chamber! This valve is simply a bicycle tube valve with rubber seals. After removing it and forcing it open with compressed air, it now works. Some people replace it with a kit from a well known VW parts supplier.

The door of the fridge never closed tightly at the top left side. It wasn't until I cut the top down that I realized why - there are wear marks on the aluminum instruction plate that indicate that the door had been hitting the air pump knob.

The difficulty in fixing this problem is that the pump needs as long a stroke as possible and the pump rod must travel far enough to fully press the ignitor without bottoming out - either inside the pump itself, or by the knob hitting the fascia. By filing slotted holes for the pump and ignitor to allow them to be mounted further back from the fascia, the pump knob now recesses fully into the fascia when the door is closed.

The screws that held the door catch plate protruded and prevented the fridge cabinet front from sitting close enough to the fridge. I countersunk the catch plate holes. Also, the fridge door did not latch tightly enough against the cabinet front to provide a good seal with the front of the fridge - so 4 layers of manila card were put under the door catch plate forcing the door tighter against the fridge front.

The work was definitely worth it! A weekend run shows that while using 12V or propane, temperatures in the fridge were never above +10oC despite ambient temperatures in the van of +32. Overnight temperature reached -4oC while ambient temperature was +17.
Tests with 110V power showed that the fridge can acheive -6oC when the ambient temperature is +18oC. It seems the evaporative type fridge can keep the temperature about 20oC below ambient temperature.

The owner takes no responsibility for anyone else making these modifications.
Photos provided by owner. Contact the postmaster for permission for use.

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F. Griffiths

Last updated September 7, 2016

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