ServiceNomad RV · Knowledge
WFCO Converter Fan Runs Constantly
When the cooling fan on a WFCO power converter runs constantly without shutting off, it typically indicates the converter is working harder than normal—either charging depleted batteries, supplying high DC loads, or experiencing elevated internal temperatures. While this isn't always a fault (the fan is doing its job), constant fan operation can signal underlying issues with the converter, batteries, or DC loads that should be investigated.
Normal Fan Operation and Heat Management
WFCO converters use a temperature-controlled cooling fan to dissipate heat generated during the conversion of 120V AC to 12V DC. The fan typically runs when the converter is in bulk charging mode (pushing maximum current into discharged batteries) or when DC loads are high. As the converter heats up, the fan engages to keep internal components cool. Once charging slows or loads decrease, the converter cools and the fan shuts off. If your batteries were deeply discharged and you recently plugged in to shore power, it's normal for the fan to run continuously for several hours while the batteries recharge. Similarly, if you're running significant DC loads (lights, water pump, furnace blower, etc.) while on shore power, the converter is supplying that power and will run warm, keeping the fan on.
Aging or Sulfated Batteries
Old batteries that have lost capacity or developed sulfation (from sitting discharged) will never fully charge. The converter continues to pump current into them, trying to reach the target voltage, but the batteries cannot accept or hold the charge properly. This causes the converter to run in bulk or absorption mode indefinitely, generating heat and keeping the fan running constantly. A technician will test battery condition using a load tester or conductance tester to verify they can accept and hold a charge. They'll also measure charging current with a clamp-on ammeter—if the converter is pushing high current for extended periods without the batteries reaching full charge, the batteries likely need replacement. Operating with bad batteries not only wastes energy but also shortens converter life due to constant heavy operation.
Phantom DC Loads and Wiring Faults
Sometimes a hidden DC load is running continuously, forcing the converter to supply power all the time. Common culprits include a stuck relay, a dome light with a bad switch, aftermarket electronics with a poor ground, or even a short circuit in the DC wiring. These loads keep the converter working, generating heat, and running the fan. A technician will use a DC current clamp to measure total load on the battery/converter system with all lights and appliances turned off. Typical parasitic draw should be very low (under 1 amp). If draw is significantly higher, they'll systematically pull fuses to isolate the circuit responsible for the load. Repairing the fault allows the converter to idle properly and the fan to shut off.
Converter Over-Temperature or Failure Symptoms
If the converter itself is failing—with aging components, failing rectifiers, or damaged circuit boards—it may run hot even under light loads. Excessive internal resistance or short circuits within the converter generate heat that keeps the fan running. In severe cases, the converter may emit a burnt smell, produce erratic voltages, or fail to charge batteries properly despite the fan running constantly. A technician will test the converter's output voltage (should be 13.2-14.4V depending on charging mode) and ripple voltage (AC component in the DC output, should be minimal). High ripple or unstable voltage indicates internal converter problems. If the converter is overheating or failing, replacement is necessary—WFCO converters are reliable but have a service life of 10-15 years under normal conditions.
💡 Prevention Tips
- Replace house batteries when they no longer hold adequate capacity to prevent excessive converter operation.
- Periodically test for parasitic DC loads to catch phantom drains before they shorten converter and battery life.
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