RVs have three different electrical systems. The 12-volt DC automotive system, the 12-volt DC coach system and the 120-volt AC coach system. Today we’re going to concentrate on troubleshooting a basic 12-volt DC coach electrical system problem. 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 to components, devices and appliances that operate on 12-volt DC electricity.
These 12-volt devices include overhead lights, the water pump, vent fans, furnace fan, range hood fan, LP gas leak detectors, stereo, 12-volt TVs and the refrigerator when it is operating in the LP gas mode. When you go camping you rely on these 12-volt items to operate properly, especially if you are 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 we are dry-camping and our 12-volt water pump quits working.
I am convinced that just about anyone can troubleshoot a 12-VDC problem, and in many cases repair the problem without it ruining your camping trip. For starters you will need a couple of basic tools to assist in troubleshooting your RV’s 12-volt DC electrical system.
1) An inexpensive 12-volt test light.
2) A digital multimeter that can test 12-volt DC electricity.
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 on hand. If you are aware of any inline fuses used on the 12-volt devices in your RV 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? With the pump turned on try opening a faucet to see if the pump starts running. 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 the coach battery or batteries are charged enough to supply power to the 12-volt devices in the RV. There are a couple of quick way to test the coach batteries. You can use the monitor panel in the TV 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. Note: 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 using the 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 12-volt 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 before you continue.
If the battery is fully charged the next step is to make sure any battery disconnect switches for the coach battery are 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 going 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 illuminates on one side of the fuse replace the fuse with the proper amperage rated fuse and try the water pump again.
If there was 12-volt DC power at both sides of the fuse check for 12-volts at the water pump switch. There should be 12-volts going to the switch, but not out of the switch until it is turned on. If there is voltage going to the switch, and the switch is operating properly check the water pump wiring for an inline fuse. If you locate an inline fuse find a good ground for the 12-volt test light and probe the wire on each side of the inline fuse. If there is only power on one side of the fuse replace the fuse with the proper amperage rated fuse and test the water pump again.
If there is power on both sides of the inline fuse check the water pump wiring connections at the wire nuts. It’s possible for connections to come loose from excessive vibration. Correct any loose wiring connections you find and try the water pump again. If the water pump still doesn’t work feel the pump 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 and see if it resets itself.
If you complete all of these tests and there is 12-volt DC power coming to the water pump motor but it still doesn’t work 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 (circuit) 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.
The steps outlined above are very basic troubleshooting procedures. If you follow these steps and cannot determine the problem it will require more advanced troubleshooting procedures. If you don’t feel comfortable performing your own maintenance or troubleshooting the 12-volt electrical system take the RV to a reputable RV repair facility to have it checked out and repaired.
Caution: Exercise caution whenever you work around 12-volt batteries. Lead acid batteries contain sulfuric acid which is extremely corrosive and can cause severe burns or even blindness. The hydrogen gas that batteries produce, when they are charging is very explosive. When you work around batteries you need to wear safety glasses and gloves, remove all jewelry and do not smoke or use any open flames.
Happy RV Learning,
Mark Polk
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