VR Tip: Troubleshooting a 12 Volt DC Problem

If you like RVs, you already know that an important part of RV fun is getting away from it all. You can simply pack up the motorhome and head out for a well-deserved rest and relaxation without having to deal with the hassles of everyday life. These rest, relaxation, and memory RV trips shouldn’t be compromised by something as simple as a 12-volt electrical problem that ruins your vacation.

If you’ve been riding in an RV for some time, you already know that a good deal of the devices and accessories in your RV are powered by 12-volt DC power. 12 volts DC or direct current is electricity supplied by RV batteries. DC electricity flows in one direction, from negative to positive. 12V DC electricity is stored in RV batteries and supplies power to components, devices, and appliances that run on 12 volts.

These 12 volt devices include ceiling lights, the water pump, ventilation fans, furnace fan, range hood fan, LP gas leak detectors, stereos, 12 volt televisions, and the refrigerator when operating on the LP gas mode. When you go camping, you rely on these 12-volt items to work properly, especially if you’re camping dry without hookups. So what do you do when one of these 12 volt items stops working?

As an example, let’s say we are dry camping and our 12 volt water pump stops working.

I am convinced that almost anyone can fix a 12VDC problem and in many cases repair the problem without ruining your camping trip. To get started, you’ll need a couple of simple tools to help you troubleshoot your RV’s 12-volt electrical system.

1). An inexpensive 12 volt test light.

2). A multimeter that can test DC power.

Both are available at local auto parts stores. You should also have electrical tape, wire nuts of various sizes, 12-volt light bulbs, and 12-volt fuses on hand. Check the amperage of the fuses used in the power distribution box and keep an assortment. If you know of any in-line fuses used in any of the 12-volt devices, keep them handy as well.

Now try to determine the last time the water pump actually worked. Did you leave the motorhome for a while with the pump running? Is there water in the fresh water holding tank? Were you working on something else that could have affected the operation of the water pump? Try to think of all possible scenarios. Something could alter your memory resulting in a quick fix to the problem.

If not, the first step is to verify that the trainer’s battery or batteries are sufficiently charged to supply power to these 12-volt items. There are a couple of ways to do a quick test of the coach batteries. You can use the monitor panel to check the condition of the coach’s batteries. To get an accurate reading, make sure the RV is not plugged into power and turn on a couple of dome lights to put a small charge on the battery. Check the reading on the monitor panel. (If you check the reading on the monitor panel when the RV is plugged in to power, you’ll get a fully charged reading.) A more accurate method is to test the battery with a multimeter. Set the meter to read 12 VDC and place the negative test probe on the negative battery terminal and the positive test probe on the positive battery terminal. A fully charged battery will read in the 12.6 to 12.7 volt range. If it reads less than 12 volts, it is below 50% state of charge and will need to be charged.

If the battery is fully charged, the next step is to make sure any disconnect switch for the coach battery is turned on. If the battery disconnect switch is on, check that other 12-volt devices on the RV are working properly. If there is 12 volts of power inside the RV, you should check the fuse for the water pump at the power distribution center. Determine which fuse is for the water pump (fuses are usually labeled) and find a suitable ground for the 12-volt test light. Test both sides of the fuse to see if it has 12 volts. If the test light only illuminates on one side of the fuse, replace it with the proper size fuse and retest the water pump. If there was power on both sides of the fuse, check for 12 volts at the water pump switch. If there is voltage and the switch is working properly, check the water pump wiring for an in-line fuse.

Find a good ground for the 12 volt test light and test the wire on both sides of the fuse. If there is power on only one side of the fuse, replace it with the proper size fuse and test the pump again. If there is power on both sides of the fuse, check the water pump wiring connections at the wire nuts. Connections may come loose due to excessive vibration. Correct loose connections and retest the pump. If the pump is still not working, feel the motor to see if it is warm to the touch. If the engine is hot, a thermal break may have tripped. Let the pump cool down and see if it resets.

If you complete all of these tests and the water pump motor receives 12 volt DC power and still does not turn on, the water pump is probably faulty and needs to be replaced.

Troubleshooting a 12 volt electrical problem in your RV is not that difficult. Follow the logical path of the device that is troubleshooting the problem and see if you can determine where the problem is. You may be able to save your well-deserved vacation, some money, and a trip to the RV dealership too.

Note: If you are not comfortable doing your own maintenance or troubleshooting the 12 volt electrical system, take your RV to a reputable repair center for inspection and repair.

Happy Camping!

Copyright 2006 by Mark J. Polk Owner of Recreational Vehicle Education 101