Dometic Temperature Controls

[Siegmann]

One thing that always puzzled me about my fridge, are the temperature controls.

Mine has the outside upper panel with five lights from cold to coldest, and the sliding sleeve on the fin in the fridge. Now I know that I can control how cold the fridge compartment gets by sliding the plastic sleeve up or down on the fin. And I can control how cold the freezer and fridge get by choosing 1-5 on the upper outside panel. But how do these two controls interact? Clearly the control on the fin is a thermister, but is there a thermostat that provides feedback to the chosen 1-5 panel setting?

[cwf]

Yes. When you change the thermistor location, you change the value that the '1-5' equals on the panel.

The temp range between fridge and freezer will vary a bit because of the "absorption" process that is used in the fridge/freezer.

[dznf0g]

I try and set the controls mid-range and then find the fin setting which achieves the coldest temp at mid range. Then use the button for normal adjustment for weather. Mine is actually OFF the fins and located on the wire shelf just below the fins. But I also have a fan blowing on the fins, which introduces another variable.

[KJRitchie]

So, for adjusting the Thermistor lower down on the fins the colder the fridge should get? I thought it was the opposite because the air would be warmer at the top of the fins and would allow the fridge to cool down more.

Kelvin

[dznf0g]

Kelvin, I'm not sure if you're talking to me, but removing the thermistor from the fins keeps it warmer, thus longer "on time" for the heater or flame. After, literally, years of observation with multiple fridge units, I have concluded that warm fridges are the result of 1) too much heat in the outside compartment, 2) short cycling of the heating units. Each cooling unit has been different in its final exact location of the thermistor, but I am convinced of my findings. My current fridge will get to 34 (off) and 37 (on) for the fridge and -4 (off) and 0 (on) for the freezer. This is on #4 of 5 settings in 80 - 90 ambients. If it is in the 70s or below I have to go down to #2 or #3 on the selector. It take a lot of experimenting, but once you find the sweet spot, they work great.

Each number on my selector is good for a 1 - 3* change in the boxes, dependent upon ambient and sun loads.

[Siegmann]

I'm still curious how the 1-5 control actually works in relation to the thermister on the fin. The way I understand it, the cooling cycle is either on or off (gas lite or electric heater on). There is no "high cool" mechanism that makes the cooling cycle colder (at given outside air temperatures and flow). The thermister in the fridge measures the temperature and the circuit board turns on the cooling cycle when needed. So do the numbers correspond to a range of temperatures that the circuit board will turn the cooling cycle on and off, and the movement of the thermister on the fin just a means to fine tune this?

But if it's really hot out, then why would a higher number be needed? If the cooling unit always cools at the same rate, and just goes on and off when the thermister calls for it? If so, then when it's hot out, the cooling cycle would just stay on longer, and you would not need to raise the number setting, if the number is just responding to the thermister.

I just do not understand how these controls work.

[dznf0g]

They aren't that sophisticated. Higher ambients just make the heat transfer less efficient. Higher settings just keep the flame or element on longer to compensate for heat absorption by the box and increased inefficiency of heat shedding of the cooling unit.

[Siegmann]

But if that is the way it works, why would someone have to put it on 2 sometimes, and then 4 other times, if is just controlled thermostatically?

[cwf]

Originally Posted by Siegmann

But if that is the way it works, why would someone have to put it on 2 sometimes, and then 4 other times, if is just controlled thermostatically?

Because pushing a button, theoretically the buttons won't wear out as fast as twisting the thermistor around... and we are lazy?

[KJRitchie]

I have observed on my Dometic 7cu/ft the displayed reading on setting 5 always seems to peg out at 32F even if the ambient temperatures are in the 30s (electric or propane). No where in the user manual does it state the fridge has a lower limit. On setting 3 it displays 40F. I never bother setting it below setting 3. It doesn't seem to matter where I position the thermistor. I've tried it on the top of the fin, bottom of the fin and laying on the shelf away from the fin. Putting a wireless thermometer on the fridge wall that is against the adjacent wardrobe it will show a few degrees cooler but depending on the how much the door is opened it may show warmer.

In the summer I run at setting 5 and in the cooler months I run it on 4 or 5. Summer humidity seems to affect the performance of these fridges so I just keep it on 5.

Kelvin

[dznf0g]

Originally Posted by Siegmann

But if that is the way it works, why would someone have to put it on 2 sometimes, and then 4 other times, if is just controlled thermostatically?

My conclusion is it just depends on the amount of heat absorption through the walls of the fridge and uneven cooling throughout the interior. I can only relate my observations over the years. And yes Kelvin, each one seems different in its performance. I can only tell you to keep experimenting.