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Troubleshooting Your RV's 12-volt DC Problems

By guest Author: Mark Polk

If you've been RVing for any amount of time you are already aware that a good portion of the devices and accessories in your RV operate off of 12-volt DC power. 12-volt DC or Direct Current is electricity supplied by the RV batteries. DC electricity flows in one direction, from negative to positive. 12-VDC electricity is stored in the RV batteries and supplies power for components, devices and appliances that operate off of 12-volts.

These 12-volt devices include overhead lights, the water pump, vent fans, furnace fan, range hood fan, LP gas leak detectors, stereos, 12-volt TVs and the refrigerator when it's operating in the LP gas mode. When you go camping you rely on these 12-volt items to operate properly, especially if you're dry camping without hook-ups. So what do you do when one of these 12-volt items quit working?

For the sake of an example let's say that we are dry camping and our 12-volt water pump quits working.

The Mastech MY68 is a fully featured auto-range digital multimeter, it is well knows for its high resolution and accuracy at low currents, you can use it to measure a few micro amps both AC and DC with less than 1.2% and 1.5% accuracy. It also has many nice features such as data hold, auto power -off, tilt back stand, test leads holder and etc. Accessories: * 9V battery (installed) * User Manual * Test leads (attached)

I am convinced that just about anybody is capable of troubleshooting a 12-VDC problem, and in many cases repairing the problem without it ruining your camping trip. For starters you will need a couple of simple tools to assist you in troubleshooting your RV's 12-volt electrical system.

  1. An inexpensive 12-volt test light.
  2. A multi-meter that can test for DC power.

Both of these are available at local auto parts stores. You should also keep some electrical tape, various size wire nuts, 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're aware of any inline fuses used on any of the 12-volt devices keep these on hand too.

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

If not, the first step is to verify that the coach battery or batteries are charged enough to supply power to these 12-volt items. There are a couple of ways to perform a quick test on the coach batteries. You can use the monitor panel to check the condition of the coach batteries. To get an accurate reading make sure the RV is not plugged into electricity and turn on a couple of overhead lights to place a small load on the battery. Check the reading at the monitor panel. (If you check the reading at the monitor panel when the RV is plugged in to electricity it will give you fully charged reading) A more accurate method is to test the battery with a multi-meter. 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 range of 12.6 to 12.7 volts. If it reads less than 12-volts it is below a 50% state of charge and will need to be charged.

If the battery is fully charged, the next step is to make sure that any battery disconnect switch for the coach battery is turned on. If the battery disconnect switch is on, verify that other 12-volt devices in the RV are operating properly. If there is 12-volt power to the interior of the RV you need to check the fuse for the water pump in the power distribution center. Determine which fuse is for the water pump (fuses are normally labeled) and find a suitable ground for the 12-volt test light. Test both sides of the fuse for 12-volt power. If the test light only lights on one side of the fuse replace it with the proper size fuse and try the water pump again. If there was power at both sides of the fuse check for 12-volts at the water pump switch. If there is voltage, and the switch is operating properly check the water pump wiring for an inline fuse.

Find a good ground for the 12-volt test light and probe the wire on both sides of the fuse. If there is only power on 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. It's possible for connections to come loose due to excessive vibration. Correct any loose connections and try the pump again. If the pump still doesn't work feel the motor to see if it is hot to the touch. If the motor is hot, a thermal breaker may have been triggered. Allow the pump time to cool off and see if it re-sets itself.

If you complete all of these tests and there is 12-volt DC power coming to the water pump motor, and it still doesn't come on, chances are the water pump is bad and it will need to be replaced.

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

Note: If you don't feel comfortable performing your own maintenance or troubleshooting the 12-volt electrical system, take your RV to a reputable repair center to have it checked out and repaired

About the Author:
Polk has a degree in Industrial Management Technology and his 30 plus years of experience in maintenance includes working as an RV technician, a wheeled vehicle and power generation mechanic, an automotive maintenance technician, Battalion and Brigade level Maintenance Officer, an RV sales manager and also in the RV financing department as the Finance & Insurance manager. Copyright 2006 by Mark J. Polk owner of rveducation101.com/

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