RV Doctor Column RV Doctor #287 Dear RV Doctor, I cannot figure out why I have no electrical power in my motorhome when trying to run off the battery, (I have two batteries). I have a 1974 Eldorado on a Chevrolet chassis. When you plug it into a generator or shoreline power everything works, but when I try to run off the battery, nothing works. The original owner took the existing onboard generator out. Could this be the problem of not having electrical power? I have flipped over the 12-volt switch and it did not make a difference. I have no owner's manual to the motor home. Are there any breaker switches or fuses that can be checked? I have checked all over the Internet for help on my motorhome and can find nothing. Thank you in advance for any help you may be able to supply me with. Kim Eboch-Lawson, (Philipsburg, PA) Kim, I am assuming you are referring to the 12-volts DC power for the lights, water pump, etc., when you say "no electrical power." If you are expecting the standard, house-type receptacles to be powered, remember, those only work when connected to 120-volts AC. The roof air conditioner, a microwave and the electric side of the refrigerator, for instance, all operate on Alternating Current. The batteries only produce Direct Current for low voltage applications. I only mention this because of the age of your motorhome. It is possible yours is equipped with a dual voltage system; meaning each lamp will contain a 12-volt DC bulb (when operating off battery) AND an additional 120-volt AC bulb (when plugged into shoreline or when on the generator). But because you also mention a switch, I'm thinking you have low voltage lamps along with other DC loads such as a 12-volt water pump to be run off the batteries or powered by a converter when AC is available. If that is the case, your converter appears to be operating properly because you do have DC while plugged in. It's my opinion you either have a faulty manual switch that switches the DC power from converter to the batteries or the battery wiring is incorrect or you have lost a ground somewhere. Be sure the batteries are properly grounded to the chassis of the RV. The switch can easily be tested by an RV technician using on Ohmmeter with the AC power disconnected. Back then it was usually located at or near the converter. If it checks out fine, further troubleshooting is in order to find the wiring dilemma. If the batteries have recently been installed or connected, I'd start there and work my way to the battery/converter switch. Dear Gary, I don't have much experience with an RV, but I do have a polypropylene gas tank on my Dodge Ram 4x4 and it has a leak in the bottom. Do you have any suggestions on repairing this without removal of tank? I have tried some of the fiberglass repair kits but they did not hold. Frank Greenway, (Savannah, GA) Frank, the good news is that polypropylene, being a thermoplastic, can be successfully welded. Cement-type repair kits, as you've found out, simply will not repair a plastic tank permanently; welding is the only viable method of a permanent repair in my opinion. Another plus, plastic welding can be performed safely on polypropylene gasoline tanks since the practice employs hot air or nitrogen rather than arcing and sparking. Simply draining the tank is all that is necessary. Remember though, the area must be clean and dry to effectively weld. The downside is that it takes specialty equipment in order to weld plastics. Check with some local RV repair facilities or your closest Camping World Center. Many facilities have plastic welding machines since the same technology is used for polyethylene water tanks and ABS holding tanks. Some RV repair shops will indeed have a welder. Finding them is the difficult task. Let your fingers do the walking first. Dear RV Doctor, can I safely lower the jacks on my motorhome with my car attached to the hitch without damaging the jacks or anything else? Many gas stations are not level and I find that I need to level my coach in order to take on the most fuel. And, if I'm dumping, in order to drain the holding tanks fully, the coach should be level. It would be a real pain to have to disconnect the car every time. Chuck Weber, (Holland, OH) Chuck, it should not pose a problem to activate the leveling system with the car attached as long as the tow bar, receiver hitch and ball mount have been properly installed. Unless you have quite a drastic angle to the "A" frame portion, the hitch will simply swivel very slightly on the ball as the coach finds its level position. Again, be sure the gas station and/or dump station is "relatively" level to begin with. I would avoid the practice if you are situated on significantly uneven pavement to begin with. Monitor the coupler/hitch area carefully as you attempt this the first time. There should be no contact between the rim of the coupler over the ball with any portion of the ball mount on the coach. If it looks as if the parts will make contact, stop the leveling process and unhook the car. And I agree, the RV lifestyle should not cause pain, but relieve it! Dear Readers, in response to a query in an earlier column, I received a couple of emails regarding the use of a vacuum truck operating at a low vacuum to evacuate the holding tanks on the RV. There was caution alerted to the fact that if too much vacuum is exerted, that which exceeds the flow of air into the tank via the tank vents, the tank could then collapse. This is true. However, it was assumed the operator of the truck, (the writer of the question), would understand the emphasis of using a very low vacuum. All that said, the old Doc would like to add this addendum to the original request for the correct procedures. In addition to verifying the tank vents are clear of obstructions, I would also recommend that the toilet flushing mechanism be held open to aid in the venting process of the solid waste, black holding tank. In the past I have used a short piece of 2-inch ABS pipe cemented to a 2-inch tee fitting to keep the toilet flush valve open and still allow air to enter the tank at the same time. Also be aware that it will more than likely be necessary to add water to each of the "P" traps in the gray waste system after evacuation. Many thanks to those alert readers who voiced their concern. Dear RV Doctor, I had to replace all the fresh water piping in my 1982 Coachmen VIP model. I replaced the old lines and then the hot lines so that there were no mistakes. But now when I turn on the cold water I get hot water for a short time, then it gets cold. What's up? Peter Jungbaer, (Nesquehoning, PA) Peter, due to the layout of some floor plans, it's not uncommon for a cold branch of the fresh water system to be very close in proximity to the cold inlet on the water heater. And without a definitive method of keeping the heated water from backing into the system piping, it's inevitable that some of the water in the cold line at the inlet will also be heated. If you are sure you have indeed replaced the piping correctly, try this; Install a one-way check valve, a backflow preventer, directly to the back of the water heater on the cold, input line. Keep in mind the direction of flow. It should be positioned so that water will flow into the water heater but not out. My guess is that some of the heated water at that inlet area is being siphoned out of the water heater and delivered to that one faucet when it's opened. To test this theory try opening any hot faucet first making sure hot water is indeed flowing. Then turn that hot faucet off and open the cold water at the questionable faucet. Chances are the problem will disappear because as the hot water was running, cold water was automatically entering the heater eliminating that small portion of heated water in the cold line. Installing the backflow preventer should eliminate this condition by prohibiting any heated water inside the tank from backing into the cold line those few, crucial inches.
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