I'm dealing with a similar problem now ith my Model RM3962/3762. Here are the diagnostics from Dometic. If you provide your model number I have the resistance for the heating element for all the models, just not in my notes.
Lower Circuit Board:
All tests are to be done with the refrigerator in cooling mode.
For AC Heating element operation, check that incoming AC voltage is present at the terminals P1 and P2 on the circuit board. If voltage is below operating range (100-132 VAC) correct the incoming AC supply issue.
Check for voltage at the heating element connection terminals P3 and P4 on the circuit board. If no voltage is present, check the fuses. If the fuse is defective, replace the fuse. If fuses are good, replace the circuit board.
If voltage is present, do not change the circuit board. Move on to the heating element
The heating element is designed to deliver a predetermined amount of heat to the cooling unit. To check a heating element, remove the heat leads from the lower circuit board and measure for proper resistance across the two leads with a properly calibrated Ohm meter. Note: This should be done with the heating element at room temperature.
You should obtain the following reading plus or minus 10%.
Model RM3962/3762: 325 Watts, 120 Volts, 44 Ohms
Verify the unit is wired correctly before condemning the Circuit Board.
Note: Terminals for incoming power and heating element may vary depending on the model. Always follow the specific wiring diagram on the unit.