ServiceNomad RV · Knowledge
RV Fridge Only Works on Propane
When an RV refrigerator cools properly on propane but fails to cool on electric mode, the issue is isolated to the 120V electric heating element circuit or its associated controls. RV absorption refrigerators have two separate heat sources: a propane burner and an electric heating element. These heat the same ammonia absorption cooling unit but operate completely independently. Understanding this helps you troubleshoot why one mode works while the other doesn't.
How Electric Mode Works
In electric mode, a 120V AC heating element (typically 300-400 watts) is energized to heat the boiler tube of the absorption cooling unit. This heat drives the ammonia-water solution through the refrigeration cycle, just like the propane burner does in gas mode. The heating element is controlled by a relay on the control board, which switches it on and off based on the refrigerator's cooling needs and the mode selection. If electric mode isn't working, either the element isn't receiving power, the element itself has failed, or the control system isn't calling for heat in electric mode.
Burned Out Heating Element
The most common reason electric mode fails is a burned-out heating element. These elements are resistive coils encased in a metal sheath that clamps around the boiler tube. Over time, thermal stress, corrosion, or manufacturing defects can cause the element to fail open (infinite resistance). When this happens, no current flows and no heat is generated—the refrigerator cannot cool in electric mode. A technician will test the element with a multimeter—it should read 300-400 ohms depending on wattage. If the reading is infinite (open circuit), the element has failed and must be replaced. Replacement is straightforward but requires removing the refrigerator or accessing it from the exterior access panel.
High-Limit Thermostat and Safety Cutouts
The electric heating element circuit includes a high-limit thermostat (thermal cutout) that protects the boiler tube from overheating. If the refrigerator runs too hot—whether from blocked airflow, low coolant, or a failed control board—the high-limit thermostat will open the circuit and shut off the heating element. Some high-limit thermostats are auto-resetting, while others require manual reset (a button on the thermostat body). A technician will locate and test the high-limit thermostat (usually mounted on or near the boiler tube) and check for continuity. If it's open, they'll determine why it tripped before resetting or replacing it. Simply resetting without addressing the cause will result in repeated trips.
Control Board and Relay Failures
The control board uses a relay to switch 120V power to the heating element. If the relay contacts are burnt, stuck open, or the relay coil has failed, the element won't receive power even though everything else is functioning. Similarly, if the control board's microprocessor has failed or lost its programming, it may not recognize the electric mode selection. A technician will verify that 120V is reaching the control board input, then test for 120V at the heating element terminals when electric mode is selected. If voltage is present at the board but not at the element, the relay or internal board traces have failed. Replacement boards are model-specific and can be expensive.
⚠️ Safety Notes
- Disconnect 120V shore power before accessing the refrigerator's electrical components—heating elements and control boards carry live voltage.
- Never bypass the high-limit thermostat—it's a critical safety device that prevents boiler tube overheating and potential fire.
💡 Prevention Tips
- Ensure adequate refrigerator ventilation to prevent overheating that can damage the heating element or trip the high-limit thermostat.
- Use a surge protector to protect the refrigerator control board from campground voltage spikes that can damage relays.
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