WITHOUT FRIDGE DEFEND YOU ARE NOT PROTECTED

Dometic & Norcold reliability and fire safety, can you live without it?

This page will help you troubleshoot Norcold heater resistance for the heating element that powers the fridge when on shore power.

Instructions: Subjects are listed on left. Click the link to the right to go directly to the subject matter on this page.

- About Norcold Heaters ARP Control & Heaters
- AC Heater Specification Heater Values
- Test Norcold Heaters How to Test
- Calculate Heater Resistance Determine Resistance
- What if One Heater Fails? Norcold Safety

The first photo is of Norcold 1200 AC heater wires, the blue arrow points to the yellow and black wires leading to the two 120VAC heaters. If one heater fails, then the fridge will not cool properly when in the AC mode (shore power). The failure of one heater can result in a dangerous situation due to the boiler overheating, only the Fridge Defend by ARP can detect this situation and help prevent what may become a safety hazard.

**The good news!** The Fridge Defend can easily detect this situation. Your boiler temperature is the
heart beat of your cooling unit boiler, click here to learn more!
By measuring the boiler temperature, you can tell immediately if an AC heater
has failed. Press the center button when in the ARP mode, the Fridge
Defend will display the boiler
temperature.

Click here for our ARP Video Operation Manual which shows Fridge Defend by ARP functions.

Fuse: | 5A (AGC type fast acting) |
---|---|

Power: | 225W per heater |

Resistance @ 72°F: | 64 Ohms per heater |

This drawing shows how to test the electric heaters for a Norcold 1200. If the ARP Control detects an overheat situation when the fridge is running on shore power (AC) it may be necessary to determine if one heater has failed? Why? One heater will not apply enough heat to drive the system. The result is that all of the ammonia in the boiler will be expended without driving the peculator pump ( Click here to see how peculator pump works ), this leads to an overheat situation. Test between each of the heater leads after removing them from the Norcold controller, as seen in this drawing. Using the table above, we see that the resistance of each heater is around 64 ohms. Next check each lead to the housing or ground of the heater. This value should be either open (OL) or in the mega-ohm range.

Also see 'What if One Heater Fails' below:

If after reading how to test your electric heaters you determine a heater replacement is necessary, we recommend replacing your heaters with a pair of OEM heaters.

The resistance for any heating element can be calculated if you know the power in Watts (W). This information can usually be found on the refrigerator specifications which are usually in the fridge door cell. The following formula will give you resistance in two steps:

We know that you will either be calculating a 12VDC or 120VAC heating element, thus we know the voltage (V).

Power = Voltage times Current → P = VI → I = P/V → for the Norcold 1200 heater: I = 225W/120VAC = 1.87A

Power = the square of current times resistance → P = (I^2)R → R = P/(I^2) → for the Norcold 1200 heater: R = 225W/(1.87)^2 = 64 Ohms

The resistance for any heating element can be calculated if you know the power in Watts (W). This information can usually be found on the refrigerator specifications which are usually in the fridge door cell. The following formula will give you resistance in two steps:

We know that you will either be calculating a 12VDC or 120VAC heating element, thus we know the voltage (V).

Power = the square of current times resistance: P = (I^2)R → R = P/(I^2) → for the Norcold 1200 heater: R = 225W/(1.87)^2 = 64 Ohms

The resistance for any heating element can be calculated if you know the power in Watts (W). This information can usually be found on the refrigerator specifications which are usually in the fridge door cell. The following formula will give you resistance in two steps:

We know that you will either be calculating a 12VDC or 120VAC heating element, thus we know the voltage (V).

Power = Voltage times Current → P = VI → I = P/V → for the Norcold 1200 heater: I = 225W/120VAC = 1.87A

Power = the square of current times resistance → P = (I^2)R → R = P/(I^2) → for the Norcold 1200 heater: R = 225W/(1.87)^2 = 64 Ohms

Power = the square of current times resistance: P = (I^2)R → R = P/(I^2) → for the Norcold 1200 heater: R = 225W/(1.87)^2 = 64 Ohms

The curve to the left is of a Norcold 1211 refrigerator boiler using the ARP Data Collection control. Following is a description of the events captured in this session:

A) The refrigerator goes through a normal cooling period with both heaters connected and working properly. The refrigerator thermostat turns on the cooling unit; the temperature rises, and then holds at about 187°C. The refrigerator cabinet temperature is 45°F.

B) One heater is disconnected, then the refrigerator is allowed to go through 3 more cycles.

C) Note that the maximum temperature is now 192°C on startup.

D) The temperature drops to 179°C rather than the 187°C with both heaters.

The refrigerator cabinet temperature is 67°F after running for 7 hours with just one heater.

**CONCLUSION**: This test needs to be performed before determining if a cooling unit has failed!

Questions?

Please use Contact Us menu below if your Norcold cooling unit is not listed, or you have questions regarding Norcold heaters &/or the Fridge Defend Control.