Tip of the Day…. DC Circuits Part 1

Tip of the Day… DC Circuits. RV have two DC circuits. One is for the towing or chassis and the other is for the house side of the RV. Both of them are 12 v DC and serviced by batteries with some kind of charging unit.

Lets start with the chassis circuit. All recreational vehicles have a chassis circuit. Some are simple and some are as complicated as a tractor trailer or transit bus. At the minimum this circuit will run the lights and break away switch. The break away switch is used to apply 12 Volts to the breaks in case of a disconnect from the tow vehicle if the RV is a towable. With the chassis circuit everything will start at the battery or batteries. From here it will go to the fuses. This is where things really get complicated. You may have multiple places for fuses. I suggest that you look for documentation. A towable will usually have fuses in a central location. Class vehicles (those with an engine) may have multiple locations. Our Class A has 7 different locations for 12 volt fuses, that I have found. These fuses will control the running lights, brake lights, turn signals, fuel pumps, wipers, horn etc. If the unit has air bags and air horns it will have fuses for them as well.

For an inspection, you just want to find out where the fuses are and make sure they are all OK and in place. It is not uncommon to remove a fuse to prevent a broken item from identifying itself.

Tip of the day… AC Circuits

Tip of the day… AC.  Electrical Systems on RV consist of 3 different circuits.  120 volts AC, 12 Volts DC for the house/trailer, and 12 Volts DC for the coach.  The 120 Volts AC is typically supplied by either the generator or shore power (don’t ask me why they call it shore power, I don’t know).

This 120 v runs the lights, microwave, tvs, stereo, refrig and air conditioners to name a few items.  Depending on the unit it may also run into an inverter and charge the house batteries.  The first place that you as the buyer want to check is the fuse/circuit breaker box.

This is the first place that the AC will be available.  You want to make sure that the circuit breakers and fuses are all operational and that no loose connections can be seen.  Next you will need a circuit tester.  This is a three prong device used to check AC outlets.  Test every outlet in the RV.  Making sure that the tester indicates correct readings.  Make sure you check the storage areas as well.  Note any outlet not reading properly.

Next you want to find the GFI circuit. This is usually in the bathroom.  It will have GFI and a test/reset switch on the outlet.  Press the test button and recheck ALL of the outlets.  Make a note of those that no longer work.  These are all controlled by the GFI Circuit that you just tripped.  Again, make sure you test the ones outside as well.  You will be surprised at the number of outlets that are wired together.

If your unit has a converter/inverter unit, it more than likely also has at least one circuit breaker.  This is a good time to test it and see what outlets are controlled by the unit.  Some will have 3 or more circuit breakers.  Test then individually so you can identify which is which.  When the lights go out because one of the kids is running the hair dryer, while the microwave and coffee maker are on, you will be glad you did this.

Tip of the day… Story

Let me tell you a story, about a not so young man and his Class A motor home. This man and his family where traveling out west on a long vacation. They had stopped outside a town in Indiana and their RV decided that the trip was way too long and it needed a break, so it refused to change out of Park. Being a little mechanically inclined this man, checked the transmission fluid, check the fuses under the hood, checked the chassis fuses, started the class A up several times after letting it sit while he tried to think was could be wrong. There was no indication of any issues. No dash warning lights, no alarms going off, the rig simply would not change gears.

So, being prepared for situations like this he called the extended warranty company and was towed to a local garage. The mechanic there promptly put the RV on the computer. Turns out like some many RVs build today that the electronics were not completely compatible and the computer could not determine the cause. Old fashion troubleshooting technics would be required. Over the course of a few days, this and that were checked out and parts removed, tested and reinstalled. Nothing it seemed would fix the problem.

Finally, the mechanic called the manufacturer. The techs talked about the problem and tested this and that until someone said check the brakes! Low and behold the brakes also didn’t work. The tech at the manufacture said that this transmission controller had to have a good brake indication, a good hydraulic lifter indication, a good engine indication and a good transmission indication or it would not shift gears.

Now with something to work on the mechanic started checking all the fuses again. First under the hood, then the chassis, then the back of the chassis, then the house fuses. All were good! On a hunch, he checked under the dash. Eureka! a set of fuses in a little black box. A 20 AMP fuse was blown! Quickly the fuse was replace and EVERYTHING work!

Moral of the story, know where all of your fuses are. When you are buying a RV ask to see where the fuses are and make sure you understand what they are for. Otherwise you may have the experience of this family. Oh the cost of this little adventure was over $2800 and 9 days of vacation time.


Air Compressors

Many RV and RVers carry air compressors. If you don’t have one, I would suggest looking at purchasing one that will work with your RV tires. Part of the daily trip inspection should be checking and filling tires prior to getting on the road.

Some RV (mostly motor homes) will come with a compressor used to inflate the air bags that act like springs on the motor home. These will have a port on the compressor or in the basement area for an external air hose. This external air connection can be used to fill tires. Make sure you have a good tire pressure gauge and use it frequently when filling tires until you know how much air the compressor is putting out.

If you need a compressor you want to get something that will put out more than enough pressure for the job. My motor home tires need between 95 and 100 psi. I purchased an 100 psi compressor and it took forever to fill a tire. Gave it to my son and upgraded to 150 psi compressor. Much faster.

Compressors are basically of two types; 12 vdc or 120 vac. This is an area that cheaper is NOT better. A cheap compressor will not hold up and will only waste your time, money and maybe safety. I carry two air compressors, a 12 vdc in the trunk of the car and a 120 vac in the motor home. Since I have a generator, I can use it anywhere and any time.

If you are buying a rig with a built in air compressor, make sure to check the pressure and operations. If the air tank has a relief valve, pull it to make sure it works. Also open the drain plug to make sure there is no standing water from condisation in the tank. If there is any water in the tank and it comes out muddy or rusty, have the tank checked by a qualified technician. Rusty tanks can explode and damage the rig.

Batteries, Part 2

There are too many types of batteries to cover here. Basically, the more expensive the battery the better and longer is should last. Maintenance free batteries simply means that you don’t have to add water as part of the maintenance.

Speaking of maintenance, what maintenance should be performed and when. If a battery is in use on a daily or weekly basis, keeping it clean and charged is most of the maintenance that will be needed. If your batteries are being used to provide a limited amount of current, a trickle charger can be used to keep them charge. Trickle chargers can be AC (house current) or solar. They provide a small amount of current to keep the batteries topped off.

If the batteries are the type with removal able caps (IE maintenance type batteries), then you will need to perform a little more maintenance every now and then. Non-maintenance free batteries will require a hydrometer. A hydrometer is used to check the specific gravity (acid to water) of the battery. Its use is to determine if you need to add distilled water or battery acid to the battery. You simply remove the cap on each set of cells and draw a little bit of the fluid into the hydrometer. It will tell you the state of the fluid. Most of the time you will need to add distilled water. Add a little at a time and retest.

If you are going to put your RV into storage for a while, remove the batteries, place them in a cool (not cold or hot) area and put a trickle charger on them. This will keep the batteries charged and ready for use. Make sure to check the non-maintenance free batteries for the proper levels once a month or so.

Finally a full charged battery should read over 13.2 volts or more when not in use and not connected to any type of charger. If the voltage drops to less than 13 volts the life of the battery is coming to an end and should be scheduled for replacement.

Batteries, Part 1

Batteries: There are two uses for batteries, coach and house batteries. Coach batteries are those that are used to start the RV. These are normal 12 v car or truck type batteries and are designed to provide a lot of amperage for a short period of time. The house batteries are deep cycle batteries which are designed to provide a lower amperage for a much longer period of time.

Most of us will understand the coach batteries and can tell when it is time to replace them. They will last 3-5 years. You can tell when a coach battery starts to go bad in that it has trouble starting the engine, cranks slow or dies pretty quickly when the lights are left on. Maintenance and inspection will be covered below.

House batteries are a little more difficult to cover simply because of the wide range of use and types available. Let’s start with the purpose. House batteries are designed to run everything in the rig, from the lights to the fans and heaters. Almost everything in the RV uses electric from the batteries. As such these need to provide current (amperage) for a long period of time. Typically the house batteries can be called on to provide current for days at a low amperage. This type of battery is call a deep cycle battery. All RV run on 12 v DC systems. However, not all RV use 12 V batteries. Many motor homes will use 6 v batteries. 6 volt batteries are often call golf cart batteries as that is a primary use for them. 6 volt batteries are designed to provide current over long periods of time which makes them ideal for RVers who want to camp without electric for a few days.

Slide Outs

Today’s tip deals with slide outs. Many of the RV today have slide outs. They help increase the living space. There are several things you need to look at when inspecting them prior to buying.
There are two sets of seals. One on the slide out and one on the main body of the rig. The one on the slide out is used when you retract the rig. It should go all the way around the slide out. You want to make sure that this seal is clean, soft, pliable and without any tears. With the slide out fully retracted you want to make sure there are no gaps anywhere around the slide out. You can test for possible leaking areas by putting strips of paper between the rig and the slide out before bringing fully retracting. If the papers pullout with no resistance, the slide out could leak in those areas.
The second set of seals is on the rig body and they are used with the slide out is extended. These will be inside the rig. As with the external seals they should be complete around the slide without tears etc. You will need to inspect these prior to fully extending the slide. Watch around the lower areas of the slide. If the slide out does not extend all the way, you will get water, dust, dirt, bugs etc in the rig from these areas.
If the slide does not seal all way around it is possible to adjust it. Contact your dealer or a certified RV repairman to have them look at what needs to be done.


When looking at a rig, be sure to check out the slides. You want to operate them and watch for how smoothly they come in and out. Once they are out, get outside and check underneath. Press against the bottom looking for soft spots. With the slides in, examine the framing around the slides. Water leaks will often leave the framing soft and spongy. Although not structural, it could lead to mold. Check the deals around the slides both with it in and out. The slide should seal completely both ways.

Transmission Fluid Analysis

Most of us realize that it is important to change the oil periodically, but how many of you change the transmission fluid? Do you even know how to check the fluid? Do you check it? Part of my pre-trip inspection is to check the transmission fluid. This is done with the engine running and after having shifted the transmission into each gear. But when is it time to change the fluid? There are numbers all over the place for when to change your transmission fluid. The two easiest ways to tell are;

1. if the fluid is not bright red, then change it.

2. Have a Transmission fluid analysis done. This is just like the engine oil analysis. Pull a sample and send it to have the fluid checked out. You will get a report that tells you what metals are in the fluid, such as:

  • Aluminum: Torque converter, the case, gear and vane pumps, thrust washers
  • Chromium: Ball and roller bearings, alloy of steel parts like gears
  • Iron: Gears, bearings, shafts, some cases, clutch plates
  • Copper: Bronze bushings, oil cooler oxides, clutch plates, brass fittings
  • Lead: Residual gear marking compound, alloy of bronze
  • Tin: Some bearing cages, alloy of bronze
  • Nickel: Clutch bands, gear/shaft steel alloy
  • Silver: Some soft friction bearings, Allison needle bearings
  • Manganese: Alloy of steel
  • Titanium: Trace wear metal

In addition to the oil type ratings such as Viscosity and Flashpoint. All in all giving you a good idea as to what is going on within the transmission and when to change the fluid.

Oil Analysis

Oil Analysis and what does it tell you. Any RV with an engine should have an oil analysis done before being purchased. This is for several reasons. The foremost is to tell you IF there is a potential issue with the engine or transmission. A standard oil analysis consist of 4 tests. Spectral – Spectral analysis will tell you what metals are dissolved into the oil. This is the warning stage. If there is a high reading of a metal then that is an indication of wear for that metal type. Note: this is dissolved metals not metal flakes or fillings. Once the metal starts to break apart, spectral analysis will NOT tell you. Fillings etc will be seen in the drain oil. The second test is the Insolubles test. This test tells you how good the filter is doing. Oil breaks down when exposed to heat and air. It starts to oxidize. This oxidation is removed by the filter. The cure for oxidation is to replace the filter. The third test is Viscosity test. Viscosity is the weight of the oil, 5W30 etc. It can change over time due to overheating, contamination, moisture and coolant getting into the oil. This is the indicator that will tell us when we have to change the oil. The final test is the Flash Point test. The Flash Point Test tell us the point at which the oil basically burns. All oil has a flash point. If the oil burns at or above the assigned flash point then everything is normal. If however, the oil burns below the flash point, it is contaminated and needs to be replaced.

This article is related to engine oil analysis. I will follow up with a transmission and a coolant analysis over the coming days. These Fluid analysis are relatively inexpensive and should be done prior to buying a used RV. They will tell you a great deal about the condition of the engine, transmission, cooling system and generator, that you can not see with the naked eye. It will be money well spent.

Home inspections for the RV

Powered by WP Robot