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RV Doctor ColumnRV Doctor #310 Dear RV Doctor, I have an early 80's, 34-foot Southwind Class A motorhome. When I drive with the dash air conditioner on there is warm air coming from my heater vent on the floorboard. I have checked everything I could think of and I can't find the cure. What's happening? L. Logue, (Bakersfield, CA) Lanny, chances are the controls for the diverter doors which open and close, thereby directing the airflow, are vacuum operated. If a vacuum hose works loose either on the manifold of the engine or at the dash heater control assembly, some diverters will not function properly. Gain access to the rear of the dash control and look for a loose or disconnected vacuum hose. Sometimes they can become brittle and leak without actually coming loose, so check carefully. It may be necessary to run a vacuum test on each hose to fully evaluate the integrity of each. A small, hand operated vacuum pump can be used to test the integrity of the hoses. Follow each hose down to the engine. Close proximity to the exhaust manifold can also cause brittleness and leaking. Reroute the hoses away from any heat source. Also, it has happened that a damper door can become stuck closed due to the foam gasket deforming over time. This causes the sticky backing of the foam to literally "tape" the door shut. I've seen it happen especially in warm/hot climates and.....let's see, you live where? Check all the damper doors to be sure they are indeed moving freely. Check also the position of the heater "H" valve under the front access door on the firewall. Manipulate and lubricate the cable from the dash control and be sure this heater valve is truly opening and closing. And be sure it is closing fully! Sometimes the cable can slip at either end and even though the dash slider moves full range, the valve itself actually stays open allowing the hot water to still circulate through the heater core. If I'm not mistaken, the "default" airflow for heaters of that vintage is through the floor registers. Of course is could be a faulty dash control assembly, though I would indeed eliminate all the other possibilities before condemning that component. Dear Gary, I need a new mattress for my older, 29-foot travel trailer. The mattress is a double size, but is different in that there is a piece cut out of one corner to make room for passage. Do you know where I can get one with this shape to it? P. Webster, (Hermiston, OR) Oh yes, the infamous corner-cut mattress. Peter, it's extremely hard to find any two RV makers using the same exact size. They all differ in some aspect; even across varying models of the same brand. There is, thankfully, a solution to your dilemma. The Perfect Fit Mattress, offered by Handcraft Mattress Company. They will custom build any style or size mattress for any RV. All they need are the dimensions for your application and this family owned and operated business will have your mattress ready in two or three weeks, typically. Call them at 800-241-7751. They will send you a brochure with all the pertinent ordering instructions. They happen to have locations on each end of the US which helps facilitate the quick turn-around time. Not only for corner-cut applications, HMC is also the source for short queens, rounded corners and any other odd-ball size you can imagine. I can still envision the weird shape of the cabover mattress in an old pickup camper I had many years ago. Dear RV Doc, I have a 1990 Georgie Boy RV. My wife and I bought it last year and enjoy it very much. However, I have noticed that the black water tank leaks when it is full. At first I thought it might be cracked but then I read an article that said that it could be other things. Can you give me an idea of what to look for? If I have to remove the tank will it be a major undertaking? J. D'Auria, (Menominee, MI) Yes, Jay, it's quite possible you have a crack at or near the top of that tank. A very close inspection is recommended. Sometimes it is possible to use a mirror and a flashlight to see on top of the tank, though that is entirely dependent on the exact installation on that particular model. I recommend draining and flushing the tank numerous times and then filling the tank with fresh water. As the tank nears capacity, closely look with the mirror and flashlight to see exactly where the leak appears first. It's common to see cracks on the sides of the tank near the top; rarer are cracks on the very top of the tank. It could simply be leaking from around the three-inch down pipe from the toilet requiring nothing more than new sealant. If it's not possible to view the top portion of the tank, then yes, it will have to be dropped. It may be suspended by hangars or angle brackets. It's not a difficult task, but it could be time consuming. Shut off any incoming water; remove the toilet and the floor flange as well as the vent pipe that extends up through the roof. It may be necessary to cut the ABS vent pipe close to the floor which necessitates the use a coupler fitting after reinstallation. It is also necessary to remove the outlet fitting and to disassemble the termination assembly. Your goal is to isolate just that one tank. There are probably electrical wires running to terminals at the different levels of the tank for the monitor panel. Be sure to label and remove these wires too. If possible, support the tank with a floor jack and simply drop it down to ground level after all components have been disconnected and/or removed. After the tank has been dropped, temporarily reinstall the termination valve to block off the outlet, support the tank and refill it once again. Now you will be able to view each side, the top and bottom of the tank during the filling process. It will soon be evident where the leak truly exists. Or the crack may be quite visible by simply removing the tank. Plastic holding tanks can be successfully welded or patched using a plastic welding machine. Not all repair shops are equipped with a plastic welder, so you may have to call around. Some patch kits may work on some ABS tanks, but I've had better success welding the tank. I would not take the risk of the patch not holding; but then again, if the leak was on the very top of an ABS tank, I might just use an ABS patch and remember to never fill the tank above 3/4 full while traveling. Keep in mind some repairs may just not be feasible under any circumstance; I.E., numerous cracks, deteriorated plastic, etc. In those extreme cases a new tank is in order.
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