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RV Doctor ColumnRV Doctor #293 Dear RV Doctor, I'm in the process of restoring a 1971 Yellowstone "Cavalier" travel trailer and, for some reason or another, the previous owner removed the holding tanks. My question is, I've found many places on-line that sell the tanks, and they all have drawings which show size, etc. But none seem to show the locations of the cut-outs for the toilet and vent pipe. Do the tanks come pre-cut or do I have to measure it out and cut the holes myself? That thought kinda scares me because in case my measurements are wrong, I'll be out a lot of money! Larry Frogner, (Tinley Park, IL Larry, since many different floor plans may use the same exact tank, they are all sold with no cutouts on the top of the tank. Though it's not an exact science, it is important to get the fittings in the right place. Here's one easy method. Turn off all incoming water to the rig and remove the toilet and floor flange completely. Locate the vent that extends up through the roof. (There should already be a hole through the floor to the tank area where the vent used to be connected). Position the new tank(s) under the coach in their exact positions. This is easily accomplished if you have access to a small floor jack. When the tanks are in the correct position, from inside the RV, use a spray can of paint to mark the hole locations for the toilet down-pipe and the vent through the floor. Keep in mind the holes through the floor will be much larger than the actual pipes that attach to the tank, but just spray paint the heck out of it down through each hole. Then simply center mark your painted locations after you drop the tank(s) again and be sure to use the correct hole-saw to drill each hole. Do not use a jig saw or scroll saw. Doing so may cause future leaks. Many tanks will come with grommet-type fittings that fit into the top of the tank and allow the 3-inch toilet drain and the smaller vent pipe to then slip into their respective grommet. Some tanks fittings may be spin-on or weld-on fittings. The grommet type is the best for the do-it-yourselfer since no other specialty equipment is necessary other than the correct size hole-saw. If they do not come with the tanks, they are readily available at any well-stocked RV parts store. Remember also, each tank will require its own vent but the two tank outlets can be coupled at one termination point. Each must have its own waste valve of the appropriate size. The black toilet tank must remain a full three inches to the end of the termination assembly though the gray water tank can be reduced to two inches or even to one and one half inches if necessary for ground clearance. Next, measure the length of down-pipe required from the toilet flange to the bottom of the grommet fitting in the fully installed tank and cut a new one of 3-inch ABS piping. Mount the flange and the toilet in the reverse order in which you removed them. Be sure the vent pipes extend up through the top of the roof at least one and one half inch. Use sealant around the pipe where it extends through the roof to prohibit odors from entering the void between the roof and ceiling. Lastly, the pros will fill the tank to flood level inside the toilet to be sure no leaks exist anywhere in the new plumbing. All in all, not a difficult job, but understandably daunting when it comes to drilling the holes. Dear Gary, I have a Duo-Therm Model # 6594 furnace in an older mobile home and once in awhile the fan for the heater fails to turn off. The heat is off and there is no gas flame but the fan runs. I do not have a wiring diagram so if you are not familiar with the problem then anything that would show the components and wiring diagram would help. Does the unit have a high and low temp limit switch? The fan starts immediately when you turn the thermostat up. Bob Leeper, (Yuma, AZ) Bob, I'm guessing your furnace is the 120-volt AC only model since it is installed in a mobile home. There are two components on that model that may be the culprit; a fan switch and a fan relay. The fan switch is simply a bimetal disc that literally makes and breaks the contact by expansion and contraction in response to heat. This fan switch is a normally open switch and snaps shut when the furnace has attained the correct temperature, closing the contact and allowing the fan motor to come on. If this switch is faulty to the point of being stuck closed, the fan would run constantly. Over time, the metal disc can become fatigued and fail so it would not be surprising if it is faulty. Replacement switches are still available at any well-stocked RV appliance repair facility. The fan relay could also be shorted and allowing current to flow directly to the fan motor. These two switches are wired in parallel, sending voltage to the fan motor independent of each other, so both should be checked. I would first suspect, however, the fan switch. To check either component, the inside unit will have to be removed from the outer casing. Be sure to remove the source of 120-volts and shut the gas off completely before attempting any removal. After replacing the faulty component, it's best to check your work by "bench testing" the furnace before reinstalling the unit back into the coach. Dear RV Doctor, I have a 1982 Pace Arrow motor home that I'm stuck with. The engine works fine but everything else is gone to heck. I am planning to strip out the usable things and get rid of the rest. I recently bought a 5th wheel trailer to live in so I'm a 100% full timer. I would like to know if it would be practical to remove the 6.5 Onan generator and carry it in the pickup truck to use when traveling or is it too heavy to be practical? Also, can the refrigerator be removed and used like a "regular" refrigerator in my friend's wood shop by hooking it up to a 12-volt power supply source? If so, what type of 12-volt power supply do I need? John Harrelson, (Carson City, NV) John, it may not be exactly practical to haul around the 6.5 Onan, or to mount it on portable skids, but it certainly is worth keeping. Onan makes a fine line of portable generators that would be better suited to carry in the back of the pickup. Perhaps you could sell the 6.5 RV gen-set or trade it in at an Onan distributor. I have, however, seen many permanently mounted pickup installations, so you might want to think about that aspect. Indeed the refrigerator can be utilized as a spare, though it would be better utilized running on LP or 120-volts AC. If 12-volts DC is the only option, I would opt for a quality 12-volt power supply from an electrical warehouse. Avoid using a battery charger or RV-type converter. For full-time operation, you will want a heavy duty, continuous operation-type power supply; preferably one you can set the high and low voltage points. Don't forget, the refrigerator will still require periodic maintenance.
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