How to Troubleshoot an RV Converter Fan

by John Cagney Nash

A recreational vehicle (RV) uses a power converter to transform 120-volt alternating current (AC) from the shore power cord or a running generator to 12-volt direct current (DC). The converter comprises diodes which supply 12-volt power to the RV, and these diodes create heat. They connect to a heat sink, usually made of finned aluminum, which drains operational heat from the diodes. When the heat sink becomes hot, a thermostat/temperature sensor circuit closes and a cooling fan switches on to cool the heat sink. If the fan fails to operate, heat build-up will damage the converter, so troubleshooting and rectifying a problem is vital.

Step 1

Disconnect power from the converter. Disconnect the RV's shore power and switch off the generator. Disconnect the feed to the 12-volt circuit.

Step 2

Remove the converter case. Manufacturers seldom produce converters intended for user diagnosis and repair, so many units do not feature removable screws or nut/bolt assemblies. If your converter case is held together by rivets or spot welds, there is every likelihood that by removing them you will invalidate any guarantee or warranty. Only do it yourself if you are an experienced, competent electrical engineer with the necessary diagnostic equipment and repair tools.

Step 3

Locate the fan. Inside the converter case will be a solenoid, several diodes, the transformer itself and the circuit board which monitors and manages the charge to the coach batteries. There may be one printed circuit board which accommodates a rectifier, a capacitor, a number of resistors and a zener diode. If you must remove this board to access the fan, take extreme care not to damage its printed circuits or any of the electronic parts. You will find two alternating current (AC) wires and three direct current (DC) wires.

Step 4

Restore 120-volt power to the converter. From this point on live components will be bare and unprotected in the very tight environment in which you are working. Be extremely careful. It is necessary to have the 120-volt power on because the fan in the converter is a 120-volt item; this is why it can only be heard running when the RV is plugged in to shore power or an operating generator.

Step 5

Test the thermostat/temperature sensor unit which controls the fan by blowing heat onto the heat sink using a hair dryer or a shrink-wrap gun. Use your test meter to confirm 120-volt power is passing to the thermostat/temperature sensor unit, and then that 120-volt power is passing from it after it heats up. If it is not, the thermostat/temperature sensor unit is faulty. With the 120-volt power on, if the thermostat/temperature sensor unit is functioning and power is conveyed to the fan but it does not start up, the fan is faulty.

Step 6

Disconnect the open converter from 120-volt power again before replacing either component.

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