Norcold troubleshooting

[weedrancher]

I’m having problems with the refrigerator in my TC. The Norcold N510.3 refrigerator is 10 years old. It worked flawlessly until approx. 6 months ago. In AC mode the refrigerator/ freezer will cool down as normal and stay at approx. 35 degrees in the refer and 4 degrees in the freezer. After approx. 30 hrs, the refer warms up to 39 degrees and the freezer warms to 24 degrees. The temps will stay high for several hours then drop back down to the original temps.
The camper is level and parked in a large carport out of the sun. The outside temps are 41 at night and 75 during the day. There are no indications of a leak and everything appears to be in good shape. I checked the resistance in the heating element and it is 55.5 ohms. I also plugged the refrigerator into an extension cord. The refer temps stayed at 35 degrees and the freezer stayed at 17 degrees. The temps seem to stay consistent in LP mode.
The closest repair shop says they can’t recreate the problem and advised me that RV refrigerators only last ten years and was time to get a new refrigerator. I declared BS and I told them I’ll fix it myself. Anybody have any idea what the problem might be and what I should replace first?

[weedrancher]

After I replaced the circuit board, I got a temperature recorder to sample the freezer temperature every fifteen minutes. With the temperature set at #4, the freezer will maintain a temp between 3-5 degrees then the temp gradually rises to 20 degrees. The cycle occurs every 50 hours and it takes 8 hours to reach the peak 20 degrees before the falls back to 3-5 degrees. This cycle seems to be more gradual and consistent than the original. With the original board, I had to set the thermostat at 8 or 9 to maintain 3-5 degrees in the freezer and 35 degrees in the refrigerator. Thanks to everyone that offered advice.

[weedrancher]

I changed the board today. It took less than an hour. So far so good. Freezer at 6 degrees and the refer at 35 degrees. I hope the problem has been solved. Thanks to all who offered suggestions to solve the problem.

[weedrancher]

Just a quick update. Freezer temp raised from 6 degrees to 27 degrees for at least 4 hours then the temp started dropping. The refer temp raised from 34 degrees to 37 degrees. I got the dinosaur board on Sunday and when I get some time, I'll swap out the boards and see what happens.

[weedrancher]

old-biscuit... Thanks for the links and your help. The circuit board should arrive today and I'll install it in the next couple of days. Being retired keeps me pretty busy. 🙂

[Old-Biscuit]

2 different thermistors were used

Part #621785 for serial numbers 9159955 and below (Unavailable????)

Part #628760 for serial numbers 9158856 and above LINK


Then there is a universal repair kit---adjustable
Norcold Snip-The-Tip (Dometic snip the tip has been around for long time now they have one for Norcold.....LINK
Not sure if applicable to your 510.3

[weedrancher]

If it is a bad thermistor, Where do I get a new one for a Norcold N510.3?

[YC_1]

I apologize for suggesting this again. My friends unit had a fan or fans mounted on a metal plate in a position that you could not see them. With the bottom cover removed the plate looked like a simple edging along the top edge of the hole. The thermistor was mounted on the forward fin and accessible via the roof vent. We peeled the screen back on one end to get to it. Hard to see it and tricky to get to.

Once found we installed a bypass switch to keep the fan going in a pinch. The actual circuit that controls it went this way. Through the main ckt board, through the front doors (fan would quit when the doors opened if activated), and of course through the thermistor.

We caught it acting up and I did my highly technical troubleshooting technique. A very gentle tap with the handle of a screwdriver on the relay that controls it fired it right up. Ta Da! New board and things have been fine for almost a year now.

[dougrainer]

Chris Bryant wrote:
I wouldn't rule out the thermistor unless you tested it while the refrigerator was misbehaving- an intermittent problem means, by definition, the parts will test good sometimes.

A defective thermistor will still test good thru all parameters. Soooo, the cheaper way is to just replace the Thermister when you have this type problem. I doubt the Circuit Board is the problem on a problem like this. People ALWAYS seem to think the Control boards are the problem. As someone who works on these RV's and have for 35 years, in the past 15 years, the OEM control boards rarely fail. Doug

[Old-Biscuit]

What the heck.......it is a 10+ yr. old RV fridge :B

Post back with the end results........

[weedrancher]

I pulled the trigger on a dinosaur board. It's only money right? Things were a lot simpler with a tent and a ice chest:)

[weedrancher]

Dougrainer… This is a roof top vented refrigerator. I have a wireless thermometer in the freezer and another in the refrigerator. I checked the accuracy and they are +/- 2 degrees of the thermometer in the glass of water. I’ll try the off/on every day to see what happens. Unfortunately, I can’t check it every hour to see when it cycles off. A temp recorder would be just the ticket if I had one.

Wasatchmtnatvr: The camper interior temps are around 60 degrees. The temps in the refer/freezer rise at various times but the only way to know if they rise between 10:00 pm and 8:00 am is to stay in it or have a temp recorder. The door gaskets are fine. Thanks for the help.

[Chris_Bryant]

I wouldn't rule out the thermistor unless you tested it while the refrigerator was misbehaving- an intermittent problem means, by definition, the parts will test good sometimes.

[wasatchmtnatvr]

Is rv interior kept heated to living temperatures? Or is rv occupied? Does rise in freezer temperatures rise about 2;00am thru 9;00 am or so? If rv interior temps follow outdoor temps. the refer may not have an on duty cycle during cold nighttime ambient temps and will not call for additional cooling. With a shared freezer with food zone box, is the gasket, door seal on freezer feel proper, or poor causing freezer zone air to migrate to refer zone? Just a thought. Your reply's are very well articulated. Thanks.

[dougrainer]

Is this refer roof top vented or is the upper vent on the sidewall? If sidewall vented, the refer is required to have an Aux 12 volt fan to exhaust the hot air out the side vent. If a side vent, your fan may be malfunctioning. The fan did NOT come as OEM from Norcold, but the RV maker was required to install one if sidewall mounted. How are you monitoring the temp change? Are you taking a air temp in the refer? If so, That is NOT a good way to monitor refer performance. It is best to monitor performance with a glass of water. This is from the operators manual for the 510. It does NOT state the time frame but may be the 30 hours instead of the larger refer 48 to 54 hours. Doug

Temperature control system (N510 models):
Although the refrigerator is not frost -free, it is made to limit frost
on the cooling fins. At regular intervals, the temperature control
system automatically melts most of the frost from the cooling
fins. The water from the cooling fins drains into a collection cup
that is attached to the back of the refrigerator. The heat of the
cooling system evaporates the water from the collection cup.