Norcold N7LX.3F can't maintain temperature on 12 or 120 volt

[All_Mountain]

Norcold N7LX.3F cooling issues on 12 and 120 volt

I have a 2022 Norcold N7LX.3F that cannot maintain refrigerator temperatures on 120 or 12 volt. Refrigerator runs fine on propane.

Refrigerator is perfectly level.
(refrigerator temperatures drift up during the day with outside temperatures in the low 80s in Florida with plenty of humidity (60 – 98%) for heat transfer) Refrigerator is in a slide out and is facing due East so it is shaded after noon every day.

Observations:
- On 120 volt the condenser heat exchanger rarely gets hot enough to close the thermal switch for the single Max Flow fan mounted underneath the condenser heat exchanger. (not the case with propane, system gets hotter and the cooling fan runs)

data plate:

-> 120 volt heating element is 300 watts
--- Norcold AC Heater part number 638374
-> 12 volt heating element is 238 watts
-- Norcold DC Heater part number 638375
-> 1750 BTU/H propane heater = 512 watts


Question 1: How can it make sense to have 3 different wattages to heat the boiler?

Early troubleshooting on 120 volt

I have bypassed the condenser coil thermal switch, so the OEM cooling fan runs 100% of the time. I also add an ARP blower fan that I own at the bottom of the refrigerator to help pull cool air into the rear refrigerator compartment and blow up towards the condenser. This fan is also running 24/7.

At 1PM yesterday the freezer was 21 F and the refrigerator was 42 F I have the refrigerator set on 9, maximum cold.
At 3:40PM yesterday the freezer was 20 F and the refrigerator was 41 F I have the refrigerator set on 9, maximum cold.
At 9:20PM yesterday the freezer was 17 F and the refrigerator was 37 F I have the refrigerator set on 9, maximum cold.
At 7AM today the freezer was 13 F and the refrigerator was 30 F I have the refrigerator set on 9, maximum cold.
At 9AM today the freezer was 14 F and the refrigerator was 33 F I have the refrigerator set on 7. (starting to warm up, current outside temperature 73 F with clouds blocking the sun)

This morning I cycled the temperature button and the refrigerator stops cooling on “7” and continues to cool on “8”. I am leaving the temperature setting on “7” so I don’t freeze my food.

Question 2: Has anyone else experienced this same issue where the refrigerator cannot maintain temperature when running on 12 or 120 volt?

Question 3: Does anyone know of a higher wattage 120v element that will fit into this refrigerator?

I will continue to update this thread as I collect more data. My plan is to reconnect the condenser thermal switch to document the refrigerator temperatures with the unit wired as it came from the factory. I am going to install a second condenser cooling fan next to the OEM. It arrives today.

I wish I had my Fridge Defender installed so I could get boiler data and control my fans with it instead of the thermal switch on the condenser. I will install it in March. I had a Fridge Defender on my 2005 Dutch Star for 5 1/2 years while living fulltime.

-

[MrMark52]

Have you dug into the shielding and insulation where the heaters are located and confirmed there is a good thermal bond between the electric heaters and the boiler?

The tubes that hold the heaters is normally welded to the boiler (and tends to be a point of failure when the boilers rupture).

FWIW - 300 watts is 1023 btu, far less than the burner input - but then hard to say how efficient the burner is at putting heat into the boiler - I would SWAG it at maybe 75%, so 1750 x .75 = 1312 btu.
In other words - I think the electric heat at this point is adequate.

What would be good to monitor is the duty cycle of the different forms of heat - is either of the electric heat cycling or on continuous?

[Old-Biscuit]

Your problem is NOT airflow........you have enough fans
Your problem is LACK of heat/enough ammonia into vapor for cooling

Cools fine on LP but not on 120VAC or 12VDC

120VAC 300W element...........have you measured the AMP Draw (2.5A) or the resistance (48ohms)
*Although propane at 1750btu = 513W.......not all of that heat generated gets transferred to boiler (waste heat) so AC & LP are roughly the same heat (325*F/350*F)
Your 120VAC 300W element should function same as LP
IF--IF element is fully functioning

As for the 12VDC Element
238W 19A 0.7Ohms
Just enough heat transferred to MAINTAIN an already COLD fridge NOT sufficient to cool fridge down (used while in transit/cold fridge/unopened---not stationary)


Measure AMP Draw (AC and DC)
Measure Resistance (AC Element & DC Element)

Check Diagnostic Screen for Stored Faults
See pg 50-52
https://myrvworks.com/wp-content/upl...ice-Manual.pdf

If good amp/resistance
TEST:
Place fridge in AC Mode
Unplug thermistor leads at lower circuit board (16 pin connector/pins 4 &2 (red/white wires)
Fridge will go into continuous cooling mode (BOS)...timed based vs temp based
Freezer & Food compartments should ge VERY Cold provided Element is functioning

[All_Mountain]

I am working towards measuring the resistance now.

Thanks for your input.

[All_Mountain]

See attached photos:

12v system:

12v supply voltage no load: 13.2 volts
12v supply voltage loaded: 11.4 volts
12v resistance measured by a 20+ year old Fuke model 73: 0.5 - 0.6 ohms

238 watts/12v = 19.8 amps
12v / 19.8 amps = 0.6 ohms

Conclusion: the wire size suppling the refrigerator has too high a voltage drop. Giving away 1.8 volts is not helping the situation. My Fluke 73 does not have enough measurement capability in the >1 ohm range but it does appear the 12v heating element has the correct resistance for a 238 watt heater. I still feel the 12v wattage should be higher. I understand the complications of higher amperage components like relays and wire sizes.

120v heater resistance: 46.9 ohms

Conclusion: 120v heater resistance measure less than 48 ohms which is good. Either the 300 watt design is inadequate or I'm not getting adequate conduction from the element to the boiler tube. I'll see if I can get my eyes on the heating element holder without burning myself as we will be camping until March 1. (the heating element is inside of the insulation so I would be suprised if that's a problem but I have been wrong many times before.)

3:20 PM temperature update:

Refrigerator: 38.1 degrees
Freezer: 21.7 F (I did just add one ice tray of ambient water into the freezer about 15 minutes ago)

These are the highest temperatures of the day as I'm using a min/max recording digital thermometer.

I did disconnect the lower blower. The upper 120mm cooling fan is still running 24/7. I have 860 watts of solar so I'm not currently concerned with the current draw in South Florida.

[Old-Biscuit]

All within specs......voltage, amps, ohms

Heat generated is not being fully transferred to boiler section

As mentioned by MrMark52.........element/holders still intact/tight against boiler tube
Just straight up conduction heat transfer
*High freezer temps indicate lack of sufficient ammonia being boiled into a vapor (freezer S/B 10*F or lower as it is first in line)

[All_Mountain]

Last night's configuration: condenser cooling fans (2), (I added a second one yesterday). Both connected to the OEM thermal switch. Everything else is OEM configuration.

[COLOR="Red"]Refrigerator was not able to cool to the set point. Note the refrigerator was ~4 degrees F warmer this morning with outdoor ambient temps down to 67 F.

I'm assuming the condenser cooling fans never came on because when the unit is "hot wired" the refrigerator can achieve 37 degree steady state temperature, freezer at 22F which obviouly is unacceptable. This tells me the cooling unit is not achievimg cold enough temperature going into the freezer to get the freezer to acceptable temperatures.

MrMark52 - see photos below. I turned the refrigerator off at 6AM after letting it run all night so I could inspect the electric heating elements per your recommendation. The 120v housing is 6 1/4" long and has a full weld to the boiler tube on the side I can see. The heating element sticks out of the bottom more than I would expect.

Old-Biscuit: I ran the diagnostics per your recommendation. There were no stored fault codes on screen 4.

screen 5: Two codes: Flame present with gas off, Service required error has occurred (I cleared all stored codes this morning)

screen 7: Thermister is sensed in range

screen 8: AC heater is energized, Divider heater is energized, Interior light is
energized

screen 9: DC voltage normal

screen 0: ACvoltage high (measured with my Fluke 73 = 124v (High is supposed to be > 135 volts

Other photos show:
- freezer and refrigerator temperatures at 6:40PM last night
- temperatures this morning at 6AM when I turned the unit off for the electric element inspection.
- temperatures this morning at 8AM when I turned the unit back on to "Auto"
- this morning's 67 F outside temperature, refrigerator facing due East (morning sun)

8AM configuration, 2/2/2023: I have both condenser cooling fans "hot wired" so they run continuously so the refrigerator will cool down faster. Refrigerator set to "Auto", running on 120 volt. Temperature set on "7" to keep refrigerator from freezing.

Thanks to both of you for your valued input!

Future investigation planned:

- Cool unit back down on 120 volts with the condenser fans "hot wired"
- Document 2/3/2023 morning temperatures
- switch to 12 volt (fans still "hot wired")
- Document 2/4/2023 morning temperatures
- Stay on 12 volt if 2/4 temperatures are acceptable and wire condenser fans to the OEM thermal switch
- Document 2/5/2023 morning temperatures
- other ideas??????

[MrMark52]

What are you using to measure refrigerator and freezer temps?

Do you have the thermocouple module for your Fluke? Or do you have a thermocouple thermometer?

Need to go to the root of the cause by placing a thermocouple on the boiler to then see and compare temps that are being applied with the different heat sources. Place as high up on the boiler as you can reach.
Once you’ve placed the thermocouple - leave it there, read and record temperatures. Somehow you will need to know if any of the heat sources have cycled relative to when the temperature reading was made.

FWIW - I fought a similar problem after having my system rebuilt - at first I was depending on what the cheap CW shelf thermometers were indicating.
Then I got my Fluke thermocouple module out - “DOH!”.

[ArtJoyce]

I would check the heater amp draw when its hot. Sometimes a heater will do strange things when operating and hot like part of the element shorting out to ground. Also check out the resistance of the heating element to ground when the two wires are disconnected, it should read open or near open.

[Old-Biscuit]

Both AC & DC Elements have a BEAD Stop that should stop the element from being inserted to far.

IF BEAD is at the top of holder and element sticks out bottom of holder then element is in correctly
*never seen installed elements on N7/N8 Polar Series

What temps are achieved using PROPANE?
Freezer/food compartment?

Fridge Defender would give you boiler temps.

[Fridge Defend]

Originally Posted by All_Mountain

Norcold N7LX.3F cooling issues on 12 and 120 volt


data plate:

-> 120 volt heating element is 300 watts
--- Norcold AC Heater part number 638374
-> 12 volt heating element is 238 watts
-- Norcold DC Heater part number 638375
-> 1750 BTU/H propane heater = 512 watts


Question 1: How can it make sense to have 3 different wattages to heat the boiler?



I wish I had my Fridge Defender installed so I could get boiler data and control my fans with it instead of the thermal switch on the condenser. I will install it in March. I had a Fridge Defender on my 2005 Dutch Star for 5 1/2 years while living fulltime.

-

I have an appointment today, so this will be brief. I have not read through the thread, so for give me if I restate what has been stated:


1) Do not use the 12VDC heater, you see that the 120VAC heater is higher wattage. Never use a 12VDC heater on a Dometic nor Norcold fridge unless you have a Fridge Defend by ARP, they over heat the boiler.


NOTE: this is a classic example on how the manuals can provide false info, just like driving does not affect the fridge.


2) Check the 120VAC supply voltage at the heater. Is there 120VAC @ 60 Hz? We have seen this issue for campgrounds with bad wiring, most often on the Dometic RM1350 and Norcold 1210, very sensitive to supply voltage. And, be sure measure down stream of controller.



3) The Fridge Defend will measure the boiler temperature, this is the best method to see what is going on.


4) The heat transfer from the LP flue tube and the electric heater pockets are the same, that is they both transfer heat through the weld. If you had a bad weld, most likely:


a) Either the cooling unit would have never worked properly, or
b) The cooling unit would not work at all because the failed weld results in a failed cooling unit (what Fridge Defend helps protect against).


5) Taking into account #4, the LP gas heats the boiler assembly all along the flue tube, thus conducts more heat into the cooling unit along a longer section of the cooing unit.


6) From #5 comes a clue, are you in low ambient temperatures? If so, this may be the issue, it is 30degF here in S. CA this morning.


7) Be sure to check the insulation in the boiler assembly, we have seen many Norcold where the insulation is improperly installed. Do your self a favor, install the Fridge Defend boiler sensor and then insulate the boiler very well.



Let us know if this helps, we are not consistent in monitoring iRV2 forum, we have a life outside of the internet


One last note, if the fridge is not cooling, then damage can be done to the cooling unit, the ammonia is the only thing that cools the boiler.


Paul and Mao

[All_Mountain]

Paul and Mao,

Thanks for your input. You, I and Mao have met several times in Arizona at the Escapees Escapade in Tucson (2019). I purchased/installed my first ARP controller in January of 2017 on my 2005 Dutch Star.

Many of the things you have mentioned I have addressed in this thread. (Greg Haymond, we have also spoken on the phone)

Yesterday I did improve how the fiberglass insulation is wrapped around the electric heating elements per your recommendation.

I spent 5 months this summer in northern Canada and Alaska only running the refrigerator on propane (most of the time) and 12v (never on 120v). Outdoor ambient tempertures were cooler than the mid 80s I'm experiencing now in Hobe Sound, Florida. The back of the refrigerator is facing due East so it is getting sun until noon. The sun us still pretty far south so at 8AM shadows are pointing to the NW so not really a terrible situation.

I ran the unit all night on 120v with two CPU type cooling fans (one OEM and one that I added as my refrigerator is in a slide out in my AF 990 truck camper) running 24/7 as the condenser coil is not getting hot enough to close the OEM thermal switch. This morning the refrigerator is at 39 F (has not achieved steady state temperature. I know this because when I switch the unit to propane I can hear the flame light). Freezer is at 16 F. Per the digital control panel on the front of the unit, in diagnostic mode, screen 3, the cooling fins in the refrigerator are at 20 F after running all night.

[Old-Biscuit]

What freezer/food temps when using LP?

When did you find out the 120VAC and 12VDC were not cooling as well as LP?


FIN Temp in food compartment S/B 10*F LOWER then compartment temps
IE: 20*F FIN=30*F

Have you TRIED running w/o the thermistor connected to test cooling capabilities?

[Fridge Defend]

Originally Posted by All_Mountain

Paul and Mao,

Thanks for your input. You, I and Mao have met several times in Arizona at the Escapees Escapade in Tucson (2019). I purchased/installed my first ARP controller in January of 2017 on my 2005 Dutch Star.



(We will be at the 2023 March Tucson Escapade in Tucson, hope to hook up with you, if you do go, and get in early, let us know.)


Many of the things you have mentioned I have addressed in this thread. (Greg Haymond, we have also spoken on the phone)


(Yes, Mao said that you contacted us about an Amish cooling unit that was not preforming? Mao is the brains, I just have the looks )


Yesterday I did improve how the fiberglass insulation is wrapped around the electric heating elements per your recommendation.



(Let is know how this works in addition to what is below)


I spent 5 months this summer in northern Canada and Alaska only running the refrigerator on propane (most of the time) and 12v (never on 120v). Outdoor ambient tempertures were cooler than the mid 80s I'm experiencing now in Hobe Sound, Florida. The back of the refrigerator is facing due East so it is getting sun until noon. The sun us still pretty far south so at 8AM shadows are pointing to the NW so not really a terrible situation.


(Do you have our #4 Kit with two blowers on the vents?)


I ran the unit all night on 120v with two CPU type cooling fans (one OEM and one that I added as my refrigerator is in a slide out in my AF 990 truck camper) running 24/7 as the condenser coil is not getting hot enough to close the OEM thermal switch.


(You just gave a very important clue, not enough ammonia at the condenser, what does the Fridge Defend fan control temperature read at this junction of troubleshooting? This is critical!)



This morning the refrigerator is at 39 F (has not achieved steady state temperature. I know this because when I switch the unit to propane I can hear the flame light). Freezer is at 16 F. Per the digital control panel on the front of the unit, in diagnostic mode, screen 3, the cooling fins in the refrigerator are at 20 F after running all night.


(You are doing a great job of providing useful data. Please take these same temperatures when using the Fridge Defend diagnostic variables to solve this problem.)

Thanks for the reminder, this is coming together now, I am sorry you are still having issues. See inline comments above in your quote, and below:



Do you have the Fridge Defend on your refrigerator?


Here is what you need to do if you have the best diagnostics for absorption refrigerator on your cooling unit.




1) Let fridge sit overnight turned off (if you can).


2) Record the ARP/Fridge Defend diagnostic variables, then clear them to record new variables that are specific to the test period.


3) Start the fridge on 120VAC, let run all day.



4) Recheck the diagnostic variables at the end of the test period.



5) Repeat the above on LP Gas mode.


6) Send the before test, 120VAC, and LP GAS values to us so we can analyze them.


Thanks for your support and kind words, Paul and Mao