We included this video on the page to show how to test the electric heaters. Although this is a different fridge, the same principles apply to all Dometic RV refrigerators. This video covers:



For those that like written instruction with details – please read on:

About Dometic Heaters

The first photo shows typical Dometic AC Heaters. This is a side-by-side model that has two AC heaters that are wired in series. There are 3 situations that can occur.
1) One heater fails open, the AC heaters will not work at all.
2) One heater develops a short and only one heater is functioning.
3) The resistance of the heaters changes with age, not enough heat is applied to the cooling unit to power the refrigeration process.

For case 2 and 3 above the cooling unit can be damaged due to the boiler overheating.

The good news! The Fridge Defend Control can easily detect this situation. Your boiler temperature is the heart beat of your cooling unit! 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. Get the Fridge Defend, the best safety and troubleshooting tool.

How to Test Dometic Heaters

We publish the heater resistance specifications by the model of Dometic fridge you have. Be sure to measure the resistance when the boiler is cool. Click here and search by Dometic model, such as DM3762, to get the resistance of the heater.

This drawing shows how to test the electric heaters for a any fridge. If the ARP Control detects an overheat situation when the fridge is running on shore power (AC) it may be necessary to determine if situation 1 or 2 above has occurred? 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 ),

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.

What if One Heater Fails?

The curve to the left is of a Dometic 3-way 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 AC heater 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) Fridge is switched to the 12VDC heater, 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 the AC heater.

The refrigerator cabinet temperature is 67°F after running for 7 hours with the 12VDC heater.

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