Digital thermostat replacement for the 2-way fridge

rh5555

From day one, we've been underwhelmed by the ability of the 2-way fridge in our TAB400 to maintain a consistent temperature.  It was only made worse when I installed an indoor-outdoor temperature monitor with the outside probe tucked in the fridge - now we could really observe wild temperature swings, and see that the fridge temperature changed with ambient temperature too.

I became intrigued with this digital thermostat controller from Amazon:

It looked like it had all the right functions to control the fridge, and so it does.  The final install looks like this

and works much, much better than the original thermostat.  You also get the convenience of being able to put the temperature sensor where you want to best keep the temperature constant, the actual fridge temperature is always displayed and changing the temperature doesn't involve unloading half the fridge.  The one downside is that the temperature of the fridge is always (brightly) displayed.  Drape clothes over this when trying to sleep!

If you want to do this mod yourself, read on.  You'll need to do a little demolition and carpentry as well a solder or crimp a few connections.

The first thing to do is remove the fridge.  This is held in place by 4 screws hidden behind white caps (that pop off when pried), 2 on each side of the inside of the fridge, near the door.  You will need to remove the drawer below the fridge (which is a little awkward) and the cutlery drawer too.  The fridge then pulls out, and you have to disconnect the 120V and 12V plugs from the back before you can get it out of the way.

Next, some demolition.  We need to first remove the trim piece into which we'll mount the thermostat controller and on/off switch.  This is held in place by one external screw around the corner under the shelf, four (if I remember correctly) screws that are really awkward to access.  They are Kreg screws angled in from above the bit of wood labelled "1" into trim piece "2".  (The bit of wood above it won't be present on your trailer - I added that later).  You'll need a right-angle ratcheting screwdriver to get to these screws.

There is one (maybe two) final screw(s) that attaches the trim piece to the rest of the cabinetry.  You cannot access it (them) and the only way to remove the trim piece is to tear them out.  Don't worry - they weren't that important, the trim piece is really secure without them.  Just pull the trim piece away from the cabinet and the screw(s) will pull out.

Once you've removed the trim piece, you can exercise your carpentry skills by cutting a hole for the controller and on/off switch.  Because the trim piece is so thick (you gotta love NuCamp) I needed to counter-bore the hole for the switch and cut grooves "3" for the clamps that hold the controller in place.  The support piece ("1") also needs to be recessed to dodge the controller and on/off switch.

Now for the wiring: The power to the controller is obtained from the same leads that power the fridge.  I connected an on/off switch in series with them so that the fridge and controller could be conveniently turned off.  The connections to replace the thermostat require a 1.5 kohm resistor in series with the switched contacts of the new controller (don't ask me why). I buried that in heat-shrink tubing.  On the back of the fridge, remove the black and white leads that go from the existing thermostat to the lower connections.  Wire in the leads from the switched output of the new controller in their stead.  Note the upper two connections need to be joined together (these are marked "C" and "P") and go to one side of the switched output, the other side goes directly to the pin marked "T".

 

Finally, reinstall the trim piece and reinsert the fridge (remembering to reconnect the 12V and 120V plugs) and replace the support screws.  Place the temperature sensor where you wish to sense temperature and you're ready to go.