Ask the RV Doctor

Q. I have a 1988 motorhome that's wired for 30 amps and has two roof air-conditioner units. Many campgrounds have 30- and 50-amp service. When running the generator, I can run both air conditioners, but when hooked up to shore power, I can only run one or the other. There's a switch under the refrigerator that switches between the two. I want to run both air conditioners when hooked up to the campground shore power.

Ronald Wade
Rockwall, Texas

A. There are aftermarket devices available that will allow you to automatically operate both air conditioners, but only one at a time. The device is wired to each air conditioner and toggles between the two units after each compressor cycles off.

Your existing 30-amp service limits the coach to one air conditioner at a time since each unit requires its 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-killowatt 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 at, (800) 251-2408.

Valve Vault

Q. My question is concerning the ground clearance for the sewer-hose coupler and dump valves. Mine seems to be insufficient. I've 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.

I have thought of skid plates as an option. I have also 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's a mandatory inspection item after every trip. Driveways and dips can be a challenge at times, and 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.

Carlos Gomez
San Diego, Calif.

A. 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.

First, completely empty and flush out each holding tank. 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. Mark and remove them all and cement them back into place. If you can't reach the valves, once they are positioned on the tank outlet, consider using electric dump valves.

PhaseFour makes the Drain Master electric waste valve. Easily installed, the valves are operated by a simple push of a button from inside the RV.

I don't recommend installing skid plates or bumper casters, which leads to other chassis-related problems. Getting the plumbing as high as possible is your best bet.

Water Pump with a Punch

Q. What can be done to reduce or eliminate excess noise and vibration when using my self-contained water system? Everything works just fine, but when the pump is being used the noise seems excessive. Will an accumulator help or just reduce the amount of time the pump is working?