Replacing our fridge. Absorption vs Residential

[Jason Worman]

Hi All,

So our absorption fridge appears to be on the way out. It either freezes up on the "max" setting or is above 40 degrees on anything less than that. It is 7.7 cubic feet so we are considering replacing with residential model. For the foreseeable future we are parked as hosts and plugged into 50 amp power. We have 2000 watt inverter if we decide to travel. I really like ours now that can run on propane. Anybody switched over to residential? How is it when traveling or dry camping?We don't have solar installed. I imagine the install is quite a job and left too

Thank you,

Jason Worman

[Bill Lampkin]

I just replaced our Norcold 1210 w/ a 18 cu/ft Fisher Paykel. For your smaller 7.7, you could look at replacing the absorption cooling unit with an 'HVAC' or residential cooling unit retrofit. See https://jc-refrigeration.com/

[Eric Maclean]

Jason
If your unit is capable of freezing up the fridge section it would appear the cooling unit is working and that your problem may be the thermistor or electronic control board which controls the temp in the fridge.
Eric

[Eric Maclean]

Jason
The temp in the fridge is monitored by a thermistor clipped to the cooling fins.
This thermistor is an NTP ( negative temperature coefficient) meaning as the temperature goes down the resistance goes up
When that resistance reaches the neighborhood of 7 to 10 K ohms this resistance signals the control board to shut down the cooling unit.
This 7 to 10 K ohms should occur at or near 34 degrees F.

With your cooling unit freezing when on Max cool it would appear the cooling unit is working .
The unit provides cooling to the freezer first and then on to the fridge compartment second so if the fridge is getting cold enough to frost the fins then the cooling unit is working.
As discribed above the thermistor controls the cooling unit via the control board on Max cooling the thermistor may be bypassed
Allowing the unit to cool but when not on Max cool the control board relies on the thermistor to control the boards decision to shut down the cooling unit.

With that logic the problem could be a bad thermistor, too high resistance could be a bad connection or corrosion on the board connection.
Disconnect and check the resistance of the thermistor at the control board if it is at or above 7000 ohm at room temperature you've found your problem.

Hope some of this helps
Good luck
Eric

[Jason Worman]

Eric,

How do I test the components that you mentioned?

Jason

[Jason Worman]

Eric,

Oops! I was to quick responding! Thank you
Jason

[Bill Lampkin]

Absorption cooling uses ammonia as refrigerant; If, when working around the back of the refrig (outside) you smell any ammonia, shut off the fridge asap and move your food to an ice chest. Your fridge is almost 30 years old (if original) and way past due for replacement. Leaking ammonia isn't so bad, but there is also some flammable hydrogen gas in the ammonia, and that, when leaking, can start a fire!

You can keep the fridg 'box' and just replace the cooling unit, for safety sake!

[Jason Worman]

Bill,

I emailed Dutch Air about needing new cooling unit. RV that did initial inspection after purchase said cooling unit had been replaced at some time.

Jason

[Eric Maclean]

Jason
As Bill mentioned a failing or failed cooling unit is usually accompanied by an amonia smell or a yellow stain or powder near the failure( leak) if you have any of these signs the unit is done and shouldn't be operated as it's a fire hazard.
But if the cooling unit will still freeze up that's not likely the case.
Eric

[Jason Worman]

Eric,
The fridge seems very solid. So is it okay to have the metal fins frozen over?
Jason

[Roy Lewis]

Our control board was out and we replaced it with a board from Dinosaur Boards out of Ore. It was a plug n play and a adjustable thermistor was built right in, seems like the $100 range.

[Keith Moffett]

Jason
Much is said about the absorbtion fridge.  You asked about a residential.
Ours came with the residential by Westinghouse (I believe).  It is original so you can take from that it has held up well for 125K miles and 3 trips to Ak.
We do have extra batteries but thats about it beyond the 2500 watt inverter. 
If you are on shore power ours is no problem.  While driving we have the inverter on so again no problem.  Dry camping is a small problem in warm weather.  We run the generator twice a day.  That is with our 2007 fridge.  I understand the new fridges draw about half the power we use.
Replacemen cost and the fire danger all considered you couldnt give me an absorbtion unit.

[Eric Maclean]

Jason
Sorry for the delay frozen over fins are a sign of moisture in the fridge usually caused by a leakly door seal letting air into the fridge with the door closed .
This can be checked using a dollar bill, just close the bill in the door and see how much pull it takes to pull it out through the door seal if there's no resistance the seal needs to be tightened up or replaced.
If the cooling unit is making ice on the fridge fins the cooling unit is working ok.
The fridge should be in the 37 degree ball park for proper refrigeration.
A bad door seal allows warmer air into the fridge and makes the fridge work harder to keep cool as the moisture condenses on the cold fins it freezes which creates an ice layer which insulates the fins somewhat from the air flow making it even harder for the fridge to keep cool.
Some people install a fan to move air over the fins to help alleviate the moisture condensing on the fins this also help cool the fridge compartment more evenly.
First check your fridge temp in the fridge

Second check the thermistor resistance readings against temp.( Replace thermistor if necessary)

Check the door seal around the whole door( correct if necessary)

Depending on the climate your in you may want to add a fan in the fridge to move air over those fins in a very humid climate this becomes more necessary.

In very hot areas it is sometimes necessary to add a fan to the rear cooling fins to help with air flow and efficiency .

And of course these fridges must be kept level to work properly if they are far enough off level they will not return the cooling solution to the boiler and the boiler will run dry this causes the anti corrosion chemical ( zinc chromate) in the solution which is a powder to cook and cristalize these crystals can then move around with the solution and plug the refrigeration office rendering the fridge in operative.( Sometimes burping the fridge will cure this problem)

Hope some of this helps
Eric

[Fred Brooks]

   Another common issue that has not been talked about is how well are the refer doors sealing. I have seen several times where the freezer is correct temperature but the refer side is 50 degrees. Seems like when folks do there spring cleaning on their RV, they remove all the shelving on the doors When they reassemble the shelves, one of them is coming in contact with the shelving inside the refer, just enough to wedge the door open at the bottom 1/8". To prove the doors are sealing properly, perform the "dollar bill test". Close the doors with a dollar bill held against the opening where it seals and then pull it out. If you feel resistance, it is sealing. If the bill falls down you have a leak. Find out what may be in the way.
  Another way to prove Eric's test on the "thermister" is to remove it from the fins. Get an ice cube and drill a 3/16 hole in it and put the thermister in the cube. Remove the thermister wire from the pc control box at the top and measure the ohms reading with a good meter. Should be 9800 to 10,000 ohms. Hope this helps, Fred

[Fred Brooks]

Me and Eric were typing at the same time,