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RV Doctor ColumnRV Doctor #264 Dear Gary, I have a 1988 Sun Crest motorhome with two roof air conditioner units. Many of the sites that we camp at have 30 and 50-amp service. The Sun Crest is wired for 30-amps. When running off of the generator I can run both A/Cs at the same time, but when hooked up to shore power, I can run one or the other but not both. There is a switch mounted under the refrigerator that switches between the two. Is this original? I would like to be able to run both air conditioners when hooked up to the campground shore power. Ideally with one on the 30-amp and the other on the 50-amp. Can you assist me with a diagram? Ronald Wade, (Rockwall, TX) Ronald, there are aftermarket devices available which will allow you to automatically operate both air conditioners, but only one at a time. The device is wired to each A/C and toggles between the two units after each compressor cycles off. Your existing 30-amp service limits the coach to one A/C at a time since each unit requires it's own 20-amp circuit. That's the reason for the "either/or" switches mounted below the refrigerator. This was the original method of manually switching between the two air conditioners while connected to a 30-amp service. With generator power, the output is such that both units can run simultaneously, (a 6.5 kw generator, for instance, can handle up to about 54-amps). The best alternative in your case is to add an energy management system such as the one found on many of the newer RVs produced by Intellitec. Wiring for both a 30-amp and 50-amp service is not practical plus it does not conform to the RV Codes and Standards. And revamping the whole coach for 50-amp service would not be cost-effective. The installation would not be too difficult since you already have all the wires you need in one place now anyway. Contact Intellitec directly, (800-251-2408), for more information. Dear RV Doc, I have a 1984 Terry travel trailer with electric brakes. The problem we are having is with the brakes. The brakes will engage when pulling it even though we do not have the brakes hooked up in the plug-in on the back of the truck. We unhooked the battery on the trailer and currently do not have this problem but it is not safe to tow the trailer without the brakes. What could be the problem? Tammy Eggen, (Laure, TX) Tammy, all travel trailers equipped with electric brakes must also be outfitted with a device called an emergency break-away switch. The purpose of this switch is to engage the trailer's electric brakes if the tow vehicle and trailer should ever become uncoupled while traveling down the highway. The power for this switch comes from the trailer battery which is why your symptoms disappear when the battery is disconnected. The switch should be located at or near the tongue of the trailer and consist of box-like device with a pin fully inserted in the switch with a long cable that attaches to the hitch of the tow vehicle. When the pin is pulled, (picture a hand grenade), the switch closes and voltage is allowed to pass to the electric brakes on the trailer. Either your pin has been pulled out or the switch is simply faulty. Break-away switches are relatively inexpensive and available at any RV supply store. They should be tested from time to time. If the pin and the cable attaching it are missing, a complete new switch should be installed. To test a break-away switch, jack up one side of the trailer and have a partner spin the tires on that side. The tow vehicle does not need to be connected for this test; a healthy trailer battery does, however. While they are spinning, pull the pin from the break-away switch - the brakes should immediately lock up. If they do not, there is an open in that circuit and further troubleshooting is in order. Jack up the opposite side and try the same test. Dear Doc, What can be done to reduce or eliminate excess noise/vibration when using my self-contained water system? Everything works just fine, but the noise when the pump is being used seems excessive. Will an accumulator help or just reduce the amount of time the pump is working? David McClintock, (Texarkana, TX) David, before jogging down and buying that accumulator, double check the installation of the water pump itself. Be sure the pump housing or motor is not touching a portion of the cabinet or other interior component. Also be sure the rubber mounts are positioned correctly. These items are probably okay, but if your RV is older, it's best to check these items from time to time anyway. Adding the accumulator will probably be your best bet. The "hammering" caused by pressure and moving water will certainly be reduced if not totally eliminated. The accumulator provides a needed cushion of air that will absorb the pounding effect you now are experiencing. It will definitely add years to the life of your pump. Dear RV Doctor, My question is concerning the ground clearance for the sewer hose coupler and dump valves. Mine seems to be insufficient. I have had to replace the gray water valve twice and reattach the coupler above the black water valve about three times in the past 18 months. In have thought of skid plates as an option. Also I have thought of using individual drain outlets, but that seems inconvenient. This is a very poor design, the termination point is just forward of the rear bumper and hangs pretty low. It is a mandatory inspection item after every trip. Driveways and dips can be a challenge at times. I have to be very selective of which gas stations I go in and out of. I wrote to the manufacturer about the design problem but never got a reply. Any suggestions or advice would be appreciated. Carlos Gomez, (San Diego, CA) Carlos, indeed some waste system designs can be lacking, especially when the coach has a long overhang behind the rear axle. The holding tanks, dictated by the floor plan design, are sometimes positioned way in the back. Here's an idea that just might gain some ground clearance. Completely empty and flush out each holding tank first. Then remove both the dump valves and all the termination plumbing. Begin by installing the dump valves directly to the tank outlets. Remember that every inch of drain line from the outlet on must drop a half inch or so for every foot of run. With the dump valves attached directly to the tank outlets, the remainder of the assembly will not hang as low. Then, just like a puzzle, connect the two outlets together as high as possible using a "wye" or sweep "tee" fitting and other ABS fittings. Be sure to "dry fit" all the pieces first. Then, mark and remove them all and cement them back into place. If you cannot reach the valves once they are positioned directly on the tank outlet, consider using electric dump valves instead of the manual type. PhaseFour makes the Drain Master electric waste valve. Easily installed, they are operated by a simple push of a button from inside the RV. Check them out at your Camping World retail store or at www.drainmaster.com. I do not recommend installing skid plates or bumper casters which only leads to other chassis related problems. Getting the plumbing as high as possible is your best bet. And keep after the manufacturer. They need to be made aware of design discrepancies!
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