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Ask Dave: Why doesn’t my 3-way refrigerator work on 12-volt?

Dear Dave,
Our camper has a 3-way fridge which works great on LP and 120-volt, but on 12-volt it seems to work but doesn’t keep the fridge cool. Temps will start out at around 32 but heats up to 45-50 as we drive. It’s a Norcold N521 SUR. Is there any way to adjust the 12 volts to put out more heat? Thanks. —HT

Dear HT,
If the refrigerator works on LP and 120-volt power, that tells me it is not the cooling unit, thermistor (temperature sensor), or module board. It has to be something in the power going to the module and ultimately the heating probe. I’m not sure what type of 12-volt heating module or probe Norcold uses. However, I would start by verifying the voltage of your house battery when the engine is running.

You did not indicate if your rig is a motorhome or travel trailer. However, either should be providing a charge to the house battery/batteries while the engine is running. Most alternators will put out 14.1 volts. This goes to the plug-in on a tow vehicle, then to a battery isolation manager (BIM) and to the house battery. A motorhome is wired directly to the BIM and to the battery, so they both should provide a charge to the house battery while driving. You can verify this using a common multimeter set to the DC setting. Start by measuring the house battery with nothing running. A fully charged battery should be at 12.6 volts. Start the engine and see if it goes up in the charge available.

If there is no increase in voltage, you might not have that feature and I would believe your house battery/batteries are draining while you are driving. According to the Norcold Service manual, they need to be 11.7 volts, at least, for the operation to start, and 10.6 volts to maintain. It may be that your refrigerator is not even starting on the 12-volt mode. I would suggest starting the engine and let it run for some time and then check for 12-volt power at the power module.

The power module is in the back of the refrigerator. If there is not an outside vent cover, you will need to remove the refrigerator. If you do have good voltage coming from the battery/batteries, take off the cover and check the 12-volt fuse inside the power module.

 

An Update: The model number was incorrectly identified and it is actually model N512 and is a three way refrigerator absorption refrigerator, not the compressor type listed previously. Having found the service manual it identifies the 12-volt operation and suggests the following;

 

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Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club

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