RV Tech Savvy: Basement Air Conditioner Units

Air conditioning for RVs

Many motorhomes on the road have a basement air-conditioning system. Several RVers I know are currently experiencing problems with their basement air system. The problem is there are no replacement compressors available for the older units. I have tried to find procedures for, or a shop that retrofits, Coleman’s model 1452-1681 basement air system (intake and exhaust vents are in different locations) to replace the present unit. Since this is a major problem for many motorhome owners, is it possible to ask the question whether someone has successfully retrofitted a Coleman model 1452-1681 unit, or know of a shop that will do the job? Also, does anyone know of a shop that installs roof braces and roof air conditioner units on motorhomes with basement air? I’m willing to pay the fee to travel and not have to worry about my air unit going out and not being able to fix it.

Edward Woodson | New Tazewell, Tennessee

This conversion should be possible with some fabrication of ducts, etc. I suggest you contact Airxcel (316-832-4357, www.airxcel.com/coleman-mach/contact-us). You might try a Google search for companies that rebuild compressors, if that is the only part you can’t find. If these steps fail, contact a good RV shop to install roof air.


Battery Disconnect Switch

My previous motorhome had a disconnect switch for both the coach and the chassis batteries, but my 2017 Winnebago Sunstar 29VE only has a disconnect switch for the coach batteries. When storing my old coach, I never had a problem with a discharged chassis battery when it sat for an extended period of time (up to six months). Is it advisable to add a disconnect switch for the chassis batteries?

Ed Gemkow | Via email

Adding a disconnect switch can help avoid a fire if rodents chew on wire insulation during storage, and can also prevent parasitic loads from discharging and damaging the battery. A simple mechanical switch located on the battery terminal is the cheapest and easiest way to go. I’m a true believer in battery disconnect switches. However, batteries do self-discharge over time. If you are going to leave them idle for as long as six months, I recommend using a maintenance charger to keep them from sulfating. If the motorhome is located where shorepower is not available, I suggest using an effective solar battery maintainer.

Brake Control Power Supply

We have a GMC Acadia that I tow behind my motorhome. The 12-volt DC power supply in the front dash has power only when the ignition is on, or when the engine is running. This is designed into the vehicle by GMC. This creates a problem when flat towing because the Blue Ox brake control needs to be plugged into a 12-volt DC power supply. I talked to two different GMC dealer service centers and was told there was nothing they could do for me by changing the system so the 12-volt DC power supply would have power all the time. They also said it would void the warranty. Have you run into this problem before and if so, what was the recommended solution?

Lawrence Cooper | Pittsburgh, Pennsylvania

Unfortunately, many dealer service personnel don’t really understand the fine print in warranties. Simply wiring the outlet so it is powered all the time would require that it be switched over from the original fuse location to a fuse that’s connected to the battery. This would NOT void the warranty for the entire vehicle. It would only negate coverage for the part that is modified, which is reasonable because you can’t expect the manufacturer to bear responsibility for someone else’s work. You might consider wiring (with a fuse) a 12-volt DC accessory receptacle directly from the battery and independent of the factory power outlet. If you don’t know how to rewire it yourself, I suggest you take it to a shop that specializes in auto electronics, or even to a shop that installs car alarms and stereo systems.

Diesel Exhaust Fluid Information

I am interested in getting information about diesel exhaust fluid (DEF). As an owner of a gasoline-powered Class A motorhome, I know very little about diesels in general and DEF in particular. But I have seen DEF become widely available — in cartons on the shelf in gas stations and at the pump in truck stops. And so I suspect that other motorhome owners would appreciate an informative article.

Oscar Wiltse | Flowery Branch, Georgia

As an owner of a gasoline engine, you really don’t need to know a lot about DEF, except to be happy you don’t need it. DEF is sprayed into the exhaust stream of diesel vehicles to break down polluting oxides of nitrogen (NOx) emissions into harmless nitrogen and water. This emission system is called Selective Catalytic Reduction (SCR) and can be found on 2010 and newer model year trucks, motorhomes and many diesel pickups and SUVs. SCR is the leading technology being used to meet 2010 and up emission regulations. SCR uses a urea-based DEF and a catalytic converter to significantly reduce harmful emissions. For every 100 gallons of diesel fuel consumed, between 2 and 4 gallons of DEF will be automatically injected into the exhaust system. The typical DEF tank in a motorhome will be approximately 15-20 gallons, thus requiring a fill every 5,000 to 6,000 miles. If the system is allowed to run out of DEF, the engine’s power is reduced, a solid red warning light will be displayed on the dash and the vehicle speed will be limited to 5 mph, or “limp home” mode, until the DEF tank is refilled.

Ford Quits When Hot

In 2016, we purchased a 28-foot 1993 Shasta Class C motorhome on a Ford E-350 chassis with a 460 engine. Back in the day, you may have had articles on the same problem we are having. On warm or hot days, after about 1-2 hours, the engine starts to bog down and eventually stalls out. After waiting about ½-1 hour, it will start and run again for about 1-2 hours. I talked with someone who had the same problem, which he couldn’t fix, and he was told it was the fuel pump. I was told it was the coil and had it replaced. Then I was told it was the fuel filter, which I replaced, but that didn’t solve the problem. I had several diagnostic tests done and no problem was found. The last time it happened, we were towed to a service center in Lake City, Florida. The service center owner said it sounded like vapor lock — big engine, small space, can’t get enough air. Makes sense. I thought Ford would have cured the problem years ago. As a temporary fix, I put two 8-inch blocks of wood under the hood to keep it propped open, with bungee cords holding the hood down, to allow more air to enter the engine. After breaking down several times in various dangerous places, I am concerned as to what is causing this. I would like to know what advice you can give me on how to cure this problem.

Jim and Carole Harper | Crawfordville, Florida

Have a tech question?Over the years, I have written several answers to owners’ letters in this column. It’s not vapor lock, so you can remove the hood blocks. When the pumps get hot they quit until they cool off. Most of the heat is radiated to the tank underneath by the engine and hot road. Ford changed the design of the pumps and came out with a wire harness modification for these units. Fuel filters should be changed regularly, but they don’t clog up when hot and then start working again normally when they cool off (as electronic components do).
So that eliminates the fuel filter as culprit. An ignition coil can malfunction when hot, but you’ve already changed it. Which leaves the No. 1 cause on these motorhomes — the in-tank fuel pump. You can verify it’s the culprit by temporarily installing a fuel-pressure test gauge, but it may have to be on there when driving, and you might have to wait until it malfunctions again. Therefore, you might want to just replace the fuel pump. You can save the installer some grief by using up most of the fuel before the tank is dropped to access the pump.

Horsepower Differences

We are planning on getting a new motorhome in the near future. I see that Ford gas Class C’s have a 305-hp engine and Class A’s have a 320-hp engine. I know that Class A motorhomes are larger. Does that use up the difference in horsepower? We are planning on using a Jeep Wrangler for our dinghy vehicle. Will both types of motorhome tow it about the same?

John Daniels | Plum Branch, South Carolina

One way to predict performance is by dividing weight by power, which gives you a power-to-weight ratio in pounds per horsepower. For estimating purposes, you could add the estimated fully loaded weight of each motorhome and dinghy combination and divide it by the horsepower rating. Keep in mind that manufacturer-published horsepower is at the flywheel, and quite a few of those horses get used up by the torque converter, transmission, driveline joints and drive axle before they get to the road. Wind drag is another factor. Class A motorhomes generally have a larger frontal area, which increases wind resistance, while Class C’s are somewhat more aerodynamic. I think you will find the differences negligible.



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