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Old 06-07-2020, 09:13 PM   #1
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How to determine electrical or liquid issue with fridge

Have a NorcoldAC/LP absorption fridge in the RV we bought in Jan, and twice have attempted to use fridge, only to be discouraged. Have read all the topics and YT videos on this, so somewhat informed that they are less than stellar units.

Before a planned weekend, I will plug in the RV the night before to cool the fridge. Next morning, the freezer will be 10-14, fridge upper 30's.
During the 1st day of travels, the temps in both sections raise a fair amount. I saw 56 in the freezer, then hung it up this weekend. We can not get any control over the temps, they fluctuate alot, but never drop back down to make the fridge usable.

I have tested the thermistor, it passed.
New burner orifice. Electric heater rod ohm'd out good.
Both LP and AC systems appear to work just fine. The circuit will change over if AC is disconnected, flame always right on cue. Tubes are hot to touch in either mode. RV is level. Vent is open thru roof vent. LP or AC, no difference.
So I am assuming the electronic side is fine, which leads to the ammonia/water mixture. Is the liquid a 'it works or it doesnt' description, or can it be intermittent? I see no yellow stains or ammonia smell. How does a DIY'r check the liquid side of the system?
My understanding is as along as the heating chamber can be heated up, the fridge should cool down. In theory, the electronics can be removed and it'll cool, the circuit board really just controls the mode selection, flame lighting, power to the AC heater rod, and turns system off/on dependant upon temp settings.
A new fridge isnt a consideration at this point. Trouble shooting the current unit will preformed till the road deadends
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Old 06-07-2020, 09:39 PM   #2
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Model would be helpful......


Some models you can disconnect thermistor and it will operate in either one of 2 modes
1) Continuously.....never shutting off
2) BOS...Backup Operating System----continues to operate but on a 'time base' vs a 'temp base'
Time base can be lengthened or shortened by changing temp setting ....higher number/longer time heat is on, Lower number, shorter time heat is on


Some models shut off if no feedback from thermistor




Unplugging electric heater element(s) and plugging the leads directly into a known working 120VAC outlet will energize element(s) continuously and test whether cooling unit is capable of cooling (all controls will be bypassed so attention must be paid to fridge operation....test should be done for at least 12 hrs)


At one point the fridge DID cool properly......10-14*F/Freezer with upper 30's/food compartment............but no longer so that sounds like a leak
Ammonia smell can dissipate fairly quickly so you may not have smelled it
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Old 06-07-2020, 10:04 PM   #3
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Model is N621. It is oldie, but rather dump a little into this one vs alot into a new one.

When I say it did work fine at 1st, then it wouldnt cool back down to usable temps, this is to say both times weekends (1 month ago and then this weekend) we tried it, it is good and cold the next morning after initial plug in. But as the weekend goes on, it goes downhill till its unusable. Did some DVM testing today and the temp was dropping in the freezer while I was trouble shooting. This was only for an hr, but it was showing me it was working. It just will not maintain the temps once it gets there.
My current line of thinking is to try a new thermister, as it will be the cheapest check, even though it tested good on the bench. I do not know how this fridge should react to a bad thermister circuit as far as your 3 different options.
Thanks
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Old 06-07-2020, 11:07 PM   #4
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N621 uses 'BOS'


When BOS is active the 'temp setting' will flash for 10 seconds when ANY button is pushed


Fridge has a diagnostic mode where you can check thermistor temp and if thermistor faulted PLus other systems
See pg 19
https://www.liveworkdream.com/wp-con...coldmanual.pdf


Circuit board could also be faulty and not controling heat cycles

Directly wiring element will test cooling units capability
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Old 06-08-2020, 04:42 AM   #5
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Perfect. Will retest with those guidelines.
Thank you
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Old 06-08-2020, 10:38 PM   #6
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The fridge may have spent some time running too far off level, and the tubes are mostly plugged.

I wouldn't waste too much time or money on it.
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Old 06-09-2020, 10:48 PM   #7
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Get a short electrical cord. Connect the wires from the element to the cord. Plug in and your cooling unit will run wide open with no interference from any of the control circuits. In a day, if it gets really cold you know the cooling unit is good. If it doesn’t, you know it’s bad.
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Old 06-10-2020, 05:40 AM   #8
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Get a short electrical cord. Connect the wires from the element to the cord. Plug in and your cooling unit will run wide open with no interference from any of the control circuits. In a day, if it gets really cold you know the cooling unit is good. If it doesn’t, you know it’s bad.
Yes. I did that very test 2 days ago. Freezer got to 45, fridge 83 over 20 hrs. Change back over to LP last nite for a double check. Checked it this morning after 12 hrs, no better, if not worse. It’s a dud.
Deciding on whether to just replacing the coil assembly with new and keep LP option, or really looking into the JC Refridgeration residential conversion.
The JC choice sounds like the best choice, and about same cost. Compressor style unit, don’t have to be worried about the levelness, faster cooling and consistent colder temps . Going 12vdc or 120vac is my next decision

The PO told us he took it in because it wasn’t working, and was informed it has to be level, which he seemed uneducated about. And I didn’t know anything then either to know otherwise. Just figured OK, make sure it’s level and it’ll be fine. Learning more everyday
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Old 06-10-2020, 05:47 AM   #9
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JC option
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Old 06-10-2020, 08:01 PM   #10
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Yes, its looking like JC will be the route I go once I decide on AC vs DC. That'll be for another discussion.

Question,
Even though the Thermistor bench tested good using heated water at different temps to check the resistance, I'm not so sure if its working while installed in the fridge. Using the control panel diagnostic procedure, the fridge control 'senses' the Thermistor when in the input mode, so I know the wiring is good. But when in the Thermister temp reading mode, it constantly is registering 64 or 68, even thought the fridge compartment is at 84*. Shouldnt the diagnostic mode reading be showing 84?

I believe I need this to be working correctly when I replace the cooling mechanics.
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Old 07-10-2020, 07:05 PM   #11
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Yes, its looking like JC will be the route I go once I decide on AC vs DC. That'll be for another discussion.

Question,
Even though the Thermistor bench tested good using heated water at different temps to check the resistance, I'm not so sure if its working while installed in the fridge. Using the control panel diagnostic procedure, the fridge control 'senses' the Thermistor when in the input mode, so I know the wiring is good. But when in the Thermister temp reading mode, it constantly is registering 64 or 68, even thought the fridge compartment is at 84*. Shouldnt the diagnostic mode reading be showing 84?

I believe I need this to be working correctly when I replace the cooling mechanics.

Mine is doing exactly the same. Have you done anything further yet?
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Old 07-13-2020, 07:45 AM   #12
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Mine is doing exactly the same. Have you done anything further yet?
Yes, I just bought the 12v hvac conversión from JC last week. Working on the install now. Once the conversion is done, I’ll revisit this thermistor discrepancy if still an issue. If so, I’ll just replace the control board and thermistor
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