RV Doctor Column RV Doctor #269 Dear RV Doctor, I have a 1982 Cobra 24-foot motorhome with a water heater problem. When I turn on the ignitor it explodes when igniting the propane, when it finally does. A loud boom! I can hear the ignitor clicking before it does light. Can you give me some suggestions? It seems to be the worst when it is a little cold outside. Dan Roberts, (Tucson, AZ) Dan, it's my hunch your unit may have a partial blockage in the curved mixing tube. Plus, I would venture your water heater is in need of what is commonly referred to as a "clean and service." All LP appliances require yearly preventive maintenance in order to remain at optimum operating efficiency. Performed each season, this set of specific maintenance procedures will minimize if not virtually eliminate all appliance operation failures. Too lengthy to list comprehensively in the column, some of the steps include setting the incoming LP line pressure, cleaning soot and carbon build-up from probes and sensors and checking/adjusting the appropriate gap spacing. In addition, cleaning electrical contacts, checking circuit board functions, etc. are all items mandated by virtually all appliance manufacturers. Specifically, I would check the LP gas pressure at the water heater and the adjustment of the primary air shutter. Misalignment of the burner tube could also lead to your symptoms. But I would look close for a blockage of sorts in the burner tube itself, impeding or disrupting the normal flow of incoming LP as it is mixed with the primary air. Dear RV Doc, I have a 2001 Bounder diesel pusher and I'm on my second battery charger for the coach batteries. Unfortunately I continue to hear a very large humming noise from the charger. Also, the charger is located just under the bed and this creates quite a problem with sleep. Is this humming normal and if so can it be moved away from ear distance for sleeping? Jack Brown, (Toledo, OH) Jack, what you are hearing is an audible mechanical resonance created by a harmonic distortion in the converter/charger. I know that sounds like double-speak, but the phenomenon is somewhat technical. I'll try to explain the happenings. Most AC electrical loads are linear, meaning the current is proportional to the AC voltage. Examples include regular AC lighting and simple motors. Linear devices rarely vary in frequency. Non-linear electrical loads, such as your AC/DC converter, can produce electrical waveforms that are multiples of the normal 60 Hertz sine wave associated with the 120-volt AC electrical system in the RV. These multiple waves, called harmonics, are actually superimposed over the original sine wave. The original, fundamental sine wave combined with any of the overlaying harmonics will result in a non-sinusoidal wave form of an entirely different shape. This is very similar to the harmonics associated with stringed musical instruments. (I could demonstrate this easier on my guitar!) This new waveform then, has the ability to create a mechanical resonance within the transformer section of the converter. Overheating of the transformer, additionally, can lead to increased levels of harmonic distortion which usually manifests itself as an audible hum via the mechanical resonance. (Hang on, we're almost there!) The laminated steel plates that make up the transformer literally begin to vibrate at a frequency that is able to be heard. Unfortunately, there's not much you can do to eliminate this resonance short of redesigning the converter to include special notch filters to block out or eliminate the offending frequencies. Sound baffles can be placed between you and the converter, but care must be taken to avoid any build up of heat in the converter area. The best cure is to simply upgrade to one of the newer, high frequency converter/chargers. They are engineered with devices that can cancel out the harmonics and allow the waveform to maintain the 60 Hertz necessary. Another benefit of upgrading is the optimum battery charging abilities available with the sophisticated, smart converter/charger. (Whew!) Dear Gary, I have a 1992 Innsbruck and all of a sudden water will not flow into the toilet. We do use a filter for all the water coming into the camper. It is a little slow in the sink and shower, too. I did clean the screens at each faucet. What else can I do? Bill Morgan, (Keithville, LA) Bill, it is quite possible the filtering media in the filter you are using has been saturated beyond its usefulness. Oftentimes filters become clogged and must be replaced with a new insert. Some have replaceable cartridges while some must simply be tossed out and replaced with a complete new filter. Not knowing which filter you are using, I would indeed at least start there. Does the problem persist whether you are using city water or the on-board system with the pump? If the problem exists only when operating the water pump, then look for another filter on the input side of the pump between the tank and the pump. Oftentimes, particles inside the water tank can become lodged in the pump filter or in the pump itself. If it happens while on city water also, look for a kink or sharp bend in the supply tubing at or near the city water inlet inside the coach. Dear Gary, I have a 26-foot motorhome in excellent condition except we had a leak in an upper window of cabover that rotted wood in the front and lower section of cabover. Local dealers tell me the cost to repair it is in excess of value of unit and haven't even quoted a repair cost. They only show me their new models. Is this worth repairing? Do I have to depend on dealers who will try to sell me another unit rather than help me fix mine? Is this type of repair more difficult? Christi Bechtold, (Litchfield, OH) Christi, unfortunately, such damage in the cabover section can be quite costly. However, for a dealer to not even quote a repair estimate while trying to steer you to a new vehicle is disingenuous at best. All reputable repair facilities will provide an estimated cost of repair and explain the pro and cons of such a repair. A thorough inspection is required in order to fully evaluate the feasibility of a repair. And keep in mind, not every RV service facility is able to perform this type of repair. I've sent you the name of a facility near you; let me know how it works out.
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