How does an RV fridge work?

[AJMike]

I am not asking about the Physics of how the fridge cools, but rather how the thermostat works to control cooling in both the freezer and refrigerator sections.

We have a 3 way fridge with separate doors and compartments for the freezer and refrigerator, but only one thermostat setting, so how does that work? Does it cool the freezer first and then the refrigerator? Does it cool both at the same time? Will it cool the refrigerator if the freezer does not need cooling?

The reason I ask is that we set out on a trip today. It is now (finally) cool here in southern Arizona and I set the temperature control to max cooling last night. This morning the freezer was rock solid cold, at about -5 F, but the refrigerator was only down to about 45 F. I thought that on our trip the refrigerator would cool down more, but it has not and is currently at 47 F. The freezer, on the other hand, has cooled down to almost -6 F, so why is the refrigerator not also dropping in temperature? Clearly it is cooling, but not by enough to drop the temperature, or even maintain it.

I am pretty sure there is nothing wrong with the propane supply as I had that fixed about 3 months ago and typically the refrigerator has operated at about 38 F, but then the freezer was at about 5 F, not -5 F. Does one have anything to do with the other? How does the temperature control (I am not sure thermostat is the right word) determine how much to cool the refrigerator?

I just don't understand the basic workings of the way it handles temperature settings between the two compartments.

[HarryStone]

On most RV fridge's, there is a thermistor mounted on a metal clip, that is attached to the fins inside of the fridge. The location of that thermistor determines the cooling.

https://www.irv2.com/forums/f258/tem...is-411366.html

[DavidEM]

With a single cooling source on your fridge, like 99% of RV fridges whether they are compressor or absorption types, the manufacturer tries to put its cooling in a place that will balance well between the refrigerator compartment and the freezer compartment.

On my fridge, an absorption style, the cooling element seems to be in the bottom of the freezer compartment but there is also a set of fins below it in the refrigerator compartment that extends the cooling there. That lets the system balance the cooling between the two compartments.

Unfortunately, it isn't perfect. You probably want your fridge to be below 40 and your freezer below 10 or a 30 degree gap. But depending on the outside climate as well as the inside temps of your RV that sometimes doesn't work as you have found.

I would adjust the thermostat to keep the refrigerator section to 40 or below and let the freezer compartment do what it is going to do.

Some home fridges have two sources of cooling and regulate the fridge and freezer compartments independently. RVs rarely do that.

David

[Old-Biscuit]

Freeze is FIRST in the process of cooling
It has to be cooled down before food compartment can begin cooling
Food compartment is SECOND in the process of cooling and therefore is the controlling factor
Thermistor of FIN in food compartment is temp sensor for Thermostat
Food compartment warms up...thermostat calls for a heating cycle
Freezer gets colder due to absorption of heat from it Then HEAT IS ABSORBED FROM FOOD COMPARTMENT

Provided that:
*Thermistor is functioning correctly...bad thermistor can cause short heat cycle for cooling...Freezer gets all the absorption/little left over for food compartment
*Circuit board malfunction....shorted heat cycles
*Cooling Unit obstruction...classic symptom of Freezer cold/food compartment NOT (caused by off level operations/damage is accumulative)

So what to do: (POST BRAND/MODEL)
*Does it have EXTERNAL FAN.....must be functional to move sufficient air across backside of fridge especially if in a slide
*Check the food compartment drip tray drain hose---should have plug in the end, no cracks in hose etc otherwise WARM Air can be pulled into food compartment and cause cooling issues
*Door seals......not fully closing/warm air gets inside. DOLLAR BILL TEST
*Unplug thermistor and run fridge W/O any temp sensing for 12Hrs
Most fridges will go into a BOS/Limb Mode where they continue to try to cool based on TIME vs TEMP
(If food compartment cools down---replace thermistor)

Still warm.....FORCE COOL TEST
*Unplug the AC Heater Element(s) Leads from lower circuit board and plug them into 120VAC Outlet (unplug Fridge AC Cord---use that outlet)
This energizes the element continuously...run for 12Hrs
MONITOR as this will Bypass ALL Controls
Food compartment gets COLD.....replace circuit board

Doesn't get COLD------------Cooling unit has blockage.