This page will help you troubleshoot Dometic AC heaters, Dometic heating element, and test Dometic heater resistance.
Instructions: Subjects are listed on left. Click the link to the right to go directly to the subject matter on this page.
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 ARP 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 ARPrv Control will display the boiler temperature.
Click here for our ARP Video Operation Manual which shows Fridge Defend Control functions.
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
),
this leads to an overheat situation.
Test between the heater leads
after removing them from the Dometic controller, as seen in this drawing.
For example, let's say by using the search 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 (use search link above) or located 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 example heater above: 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 (easiest to use the search link given above) 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 example above: R = 225W/(1.87)^2 = 64 Ohms
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!
Questions?
Please use Contact Us menu below if your Dometic cooling unit is not listed, or you have questions regarding Dometic heaters &/or the Fridge Defend Control.