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Old 05-29-2014, 12:45 PM   #1
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Dometic Fridge OK on shore power, not OK on gas

When I'm running on 120V shore power the fridge is plenty cold. When running on LP the freezer is cold enough to freeze water but refrigerator isn't as cold as on AC. Burner is lit and flame looks OK. Any ideas or suggestions?
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Old 05-29-2014, 05:05 PM   #2
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I have to ask this: Are you checking the fridge temp with your hand or a thermometer? My understanding is that an RV fridge works on "heat absorption" rather than creating cool circulating air as a home fridge does. IF there is nothing in the fridge then it may feel as if it is not cooling properly. I had somewhat this same problem with my units fridge after I bought this used unit. I leave my unit hooked up when it's in the back yard to allow the fridge to run on a low setting. My fridge didn't "feel" as if it were cold enough yet the freezer felt fine. When I mentioned this to a friend of mine who has had an RV for years he told me to put as many water bottles in the fridge as I could. Even filling old milk jugs with water would be good for it I was told. That worked! For some reason having the fridge cool the water bottles down made it seem to work better. And- -I have cold water bottles at hand when I'm working outside.
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Old 05-29-2014, 05:17 PM   #3
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Thanks for the tips. My test for the temperature has been to hold and taste a beer that's been in there. Will try to put more inside, like you say, water bottles make sense. or a full case of beer, though those have a tendency to disappear
Also heard that increasing the airflow from the side vent to the roof vent can help so am looking into solar fans that are used to do that. Anyway, appreciate the response. Happy summer!
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Old 05-29-2014, 05:21 PM   #4
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Normally, it is the other way around. The propane has a much higher and faster heat transfer to the boiler and thus cools much more quickly than the AC heater element.

For AC to be better means the flue might be blocked with something (perhaps a wasp/bug nest) limiting heat transfer due to wasted heat coming out the bottom instead of up the flue.
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Old 05-29-2014, 05:27 PM   #5
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Yep, planning to look in there and clear out any obstruction. That's what I've heard though that the LP usually works better than the AC. Thanks.
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Old 05-29-2014, 07:14 PM   #6
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Can't happen - the method for cooling the freezer and frig is exactly the same regardless if on propane or electric.

What is happening is the thermister that controls the temp is on the fins at the top of the frig portion. By adding "stuff" you make the inside of the frig warmer signaling the frig to produce more "cold". It will do so until the temp reaches the preset level and it will stop cooling. The end result is the "stuff" in the frig cannot get any colder than the preset level whether you have got one or many "stuffs".
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Old 05-29-2014, 07:29 PM   #7
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OK, so something is triggering the thermister to think it's gotten cold enough. putting warm stuff near the thermister should trigger it to cool more...maybe. Another clue. thanks.
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Old 05-29-2014, 07:39 PM   #8
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I am sure you will see a 3-5į difference between when to turn on and when to turn off. However it is hard to believe that adding jugs of water make a huge difference. It only gets as cold as it gets. Disable the thermister and it will freeze everything in the frig.
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Old 05-29-2014, 07:45 PM   #9
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Quote:
Originally Posted by cadman99 View Post
Can't happen - the method for cooling the freezer and frig is exactly the same regardless if on propane or electric.
With greatest respect, you are correct that the method for cooling is the same; Heat, from whichever source, "boils" the ammonia in the reservoir when cooling is needed.

Just saying, like heat from an electric range vs a gas range, the gas flame will get get the water in the pan to boiling quicker than the electric element on High. The water will not care as it boils at 212 degrees F; just it will reach it faster on gas.

In this case, if the available heat from the propane is being diverted (or corrupted - reduced - by a bad mixture), the AC heater might out perform the gas flame; which is normally not the case.

The "ON" time of the heat is dependent on the outside air temperature.
The hotter it is outside, the more often you will need to cycle the coolant.

The worse the efficiency of the heat source, the "warmer" the interior of the fridge will be for the same "fin" thermistor setting.

Obviously, if allowed to stabilize, the temperature inside will be identical. The wild card is the "weather" and the amount of cooling actually needed to maintain that temperature.

Hope that explains what I am trying to say, better.
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Old 05-29-2014, 07:45 PM   #10
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Things seem to be pointing at that thermister and it makes sense, but why doesn't it act that way on AC? Will look at it when I get back to the rig and mess around there a bit too.
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Old 05-29-2014, 07:50 PM   #11
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Thanks Herk for the explanation too. Wish I was at the MH now to try a few things but can't so am taking all these comments in so as to solve the problem of the warmish beer. All appreciated.
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Old 05-29-2014, 09:06 PM   #12
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Who knows?? I am sure that running on gas the frig cools faster. I am also sure that the thermister controls the inside temp of the frig. (A thermistor is a type of resistor whose resistance varies significantly with temperature). In either case the inside temp of the frig will end up the same. Can you fool the thermister - sure - if it gets warm it signals a cooling cycle.

When the thermister fails it will usually not signal a cooling shutoff and then it will freeze the entire frig. (I have had a gallon of frozen milk). Ambient temperature will definitely influence the overall efficiiency of any cooling system.

However this discussion was more cooling on electric than gas - basically can't happen.
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Old 05-30-2014, 06:08 AM   #13
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Quote:
Originally Posted by cadman99 View Post
Who knows?? I am sure that running on gas the frig cools faster. I am also sure that the thermister controls the inside temp of the frig. However this discussion was more cooling on electric than gas - basically can't happen.
Thanks for the refresher on Thermistors and you are correct, the location of the thermistor on the cooling fin determines the inside temperature,regardless of whether it is running on AC or Propane, since there is only one.

All things being equal the temperature, stabilized, should be identical whether on AC or propane heat. The OP says they are not. The only variable here is the efficiency of the ammonia bulb heat. My point is that something is effecting the transfer of thermal energy from the gas flame to the bulb. A misaligned flame, bug nest clogged flue (the AC does not use the flue), bad mixture (yellow flame), etc.

Basically, CAN happen ...
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Old 05-30-2014, 06:33 AM   #14
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Others have discussed the fridge on LP vs 120v.
I guess the LP burner might be hotter so it boils the ammonia faster and
this might give better cooling.
Why yours works better on AC is a mystery!

I can tell you that I have a couple of beer mugs that have blue ice type
fluid in them. I put them in the freezer and they are awesome!!
Pour in a 40 deg beer and it will get an ice skim on top within a few minutes!
I love mine!! BTW-- I use a thermometer and my fridge is pretty consistent at 40 in the fresh food area and really cold in the freezer. Ice cream is usually hard as a rock!

Good luck!
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