RV Mechanical Repair and Systems Service in Orange County

The Three Power Systems Living in One Coach

Almost every motorhome and travel trailer carries three electrical systems that share a floor plan and very little else. The chassis 12 volt system runs the starter, the engine controls, the dash, and the exterior lighting off the vehicle battery. The house 12 volt system runs interior lights, the water pump, furnace and refrigerator control boards, slide motors, and leveling jacks off a separate battery bank. The 120 volt system feeds outlets, roof air, the microwave, and the converter whenever the coach is on shore power or the generator is running.

Those three systems meet at a small number of parts, and almost every confusing electrical complaint starts at one of them. A battery isolation solenoid or a DC to DC charger links chassis to house. The converter turns 120 volt input into house 12 volt output. An inverter runs the other direction. An automatic transfer switch decides whether shore power or generator power reaches the panel. When one of those parts fails halfway, symptoms appear in a system that is not actually broken.

That is why we test in a fixed order. Battery state of charge and resting voltage first, then voltage under load, then the ground path, then the device itself. Skipping to the device is how people end up replacing a converter that was never bad. The chassis battery reads 12.7 volts at rest and 9.8 volts while cranking, and the problem is a cable end, not a battery. The order of testing is most of the job.

• Chassis 12 volt: starter, engine control module, dash gauges, running lights
• House 12 volt: interior lighting, water pump, furnace board, slide and jack motors
• 120 volt: outlets, roof air, microwave, residential refrigerator, converter input
• Bridge parts: isolation solenoid, DC to DC charger, converter, inverter, transfer switch
• Shared weak point: chassis and house grounds landing on painted or corroded steel

How the LP System Feeds Heat, Cooking, and Hot Water

Liquid propane leaves the tank as a liquid, boils to vapor, and passes through a two stage regulator that has to hold the coach side at roughly 11 inches of water column. That is a low pressure, and a manometer is the only honest way to read it. A regulator that has drifted down to 9 inches makes a furnace short cycle and a cooktop burn lazy and yellow. A regulator that has drifted high makes the same appliances soot. Owners usually blame the appliance. We test the regulator first.

After the regulator, the LP line branches to the furnace, the water heater, the cooktop, the oven, and on many coaches the absorption refrigerator. Each of those has an orifice sized in thousandths of an inch, and each of them collects spider webs in the burner tube during storage. A furnace that lights, runs 30 seconds, and shuts down is usually a sail switch or a partly blocked burner, not a bad board. A water heater that lights on LP but stays cold on 120 volts has a bad element or thermostat on the electric side only.

We also run a timed lock up test on the whole system before the coach leaves. Pressurize, close the tank valve, and watch the manometer for a set period. If the reading falls, there is a leak somewhere in the line, and we soap every fitting until we find it. A slow LP leak in a stored coach is the failure that turns into something much worse than a repair bill, so this test is not optional on any job that opens a gas line.

Fresh Water, Waste, and the Plumbing Between Them

The fresh side starts at either the pump or the city inlet. The pump pulls from the onboard tank and holds pressure through a built in switch, usually cycling around 45 psi. The city inlet takes whatever the campground gives it, and campgrounds sometimes give 90 psi. That is why an inline regulator set at 40 to 50 psi is the cheapest protection in the trade. Most of the split fittings and blown toilet valves we replace were killed by unregulated city pressure, not by age.

PEX runs behind cabinets and under the floor with crimp rings or expansion fittings. A leak at a crimp ring drips down a wall and shows up ten feet away as a soft spot in the floor, which is why we trace water uphill instead of patching where we see it. On the waste side, gray and black tanks drain through gate valves that stick when the seals dry out, and the vent stack has to breathe or the toilet gurgles and the tank reads wrong.

Level sensors are the most common complaint and the least common actual failure. Probes on the inside of the tank get bridged by paper and residue, so the panel reads three quarters when the tank is empty. That is a cleaning problem. A real sensor failure is a broken wire at the probe or a corroded board, and it takes a meter to tell the difference. We check probe resistance before anyone starts talking about replacing a tank.

• Fresh side: pump, accumulator, PEX runs, city inlet, backflow check
• Regulator: hold city pressure at 40 to 50 psi to protect fittings and valves
• Waste side: gray and black tanks, gate valves, seals, vent stack
• Common leak points: pump fittings, toilet supply, water heater inlet, tank flange
• Sensor faults: paper and residue bridging the probes, not a failed tank

Roof Air, Furnaces, and the Ducting Between Them

A rooftop air conditioner is a sealed system with a compressor, a fan motor, and a run capacitor, and the capacitor is the part that fails first. A unit that hums and trips the breaker almost always has a capacitor that has lost capacitance or a compressor with locked rotor. We clamp the amp draw on startup and compare it to the data plate. A 13,500 BTU unit that pulls 12 amps steady is healthy. The same unit pulling 20 amps and climbing is on its way out.

Furnaces follow a strict sequence. The thermostat calls, the blower spins up, the sail switch closes when airflow is proven, the gas valve opens, the igniter sparks, and the flame sensor confirms. Break any link and the furnace either does nothing or runs the blower and shuts down. Most no heat calls are a sail switch that will not close because the return air path is blocked by storage boxes, a dirty blower wheel, or a duct that came loose behind a cabinet. That is a cheap fix once somebody actually looks.

Ducting matters more than people expect. RV ducts are thin, taped, and easy to crush during a slide repair or a floor replacement. If one bedroom never gets cool and the rest of the coach is fine, we are looking for a collapsed duct or a missing divider in the plenum, not a weak air conditioner. Measuring temperature drop across the evaporator and again at each register tells us whether the problem is the machine or the path it feeds.

Running Gear, Brakes, and What Carries the Weight

Most towable trailers use electric drum brakes. A magnet in each drum pulls against the armature surface when the controller sends voltage, and the shoes wedge outward. Brakes that grab on one side are almost never a controller problem. They are a magnet with a shorted winding, a scored armature surface, or shoes that were never adjusted after the last replacement. We measure magnet resistance at each wheel and compare all four before anyone touches the controller in the tow vehicle.

Bearings are the other half of the axle story. Repack interval depends on how the trailer is used, but a hub that runs hot after an hour on the road is telling you the seal failed and the grease left. Dexter and Alko axles both use standard bearing sets and the parts are not expensive. The damage from ignoring it is expensive, because a spun bearing takes the spindle with it and then a whole axle gets replaced instead of a twenty dollar seal.

Suspension wear shows up as tire wear. Worn shackle bushings and a tired equalizer let the axles shift out of parallel, and the tires scrub sideways every mile. If the inside edge of one tire is feathered and the others look normal, we measure axle spacing and check the shackle holes for elongation. On motorhome chassis we look at bushings, sway bar links, and steering play before anyone spends money on a steering stabilizer that only masks the symptom.

• Trailer brakes: magnets, shoes, drums, and controller output measured at the connector
• Bearings: repack interval, seal condition, hub temperature after a road run
• Suspension: shackles, equalizer, bushings, U bolts, spring center bolts
• Tires: date codes checked against actual scaled axle weight
• Tracking: bent spindle, shifted axle, or elongated shackle holes

Why One Bad Ground Looks Like Four Unrelated Problems

Here is the failure that teaches owners the most. A coach comes in with four complaints: the water pump runs slow, the LP detector chirps at night, the step motor stalls halfway, and the refrigerator control board throws a code. Four systems, four different suppliers, four different service manuals. The actual fault is one house ground strap landing on a painted frame rail that has corroded under the ring terminal. Every one of those loads is trying to return current through a connection with resistance in it.

Resistance in a ground behaves like a hidden resistor in series with everything downstream, and Ohms law is unforgiving at 12 volts. If a corroded ground has half an ohm of resistance and the water pump pulls 8 amps, the ground alone eats 4 volts. The pump sees 8 volts instead of 12 and runs slow. The step motor stalls under load for the same reason. The refrigerator board sees a reference voltage that moves around and reports a fault it cannot explain.

Finding it is a voltage drop test, not a continuity test. A meter set to ohms will read a corroded ground as nearly zero because it pushes almost no current through the joint. Instead we load the circuit and measure across the connection while it works. Anything over about 0.2 volts across a single ground connection under load is a bad ground. That test takes ten minutes and it is the clearest reason we bill diagnostic time separately. Four parts were never the answer.

What Diagnostic Time Costs and Why It Is Billed

Diagnostic labor bills at $285 per hour. That rate covers a technician plus a scope, a clamp meter, a manometer, refrigerant gauges, and the shop time to reproduce a fault that may only happen when the coach is warm or the slide is halfway out. When you authorize the repair, the first diagnostic hour is credited against that repair. If you take the findings elsewhere, you paid for real work and you own a written report of what was measured and where.

There is also a $150 RV systems assessment. That is the broad pass, not the deep one. We check battery health, converter output, LP regulator pressure, water heater and furnace operation, roof air amp draw and temperature drop, water pump pressure, tank sensor behavior, and brake magnet resistance, then hand you a prioritized list. It is credited against an authorized repair as well. Owners buying a used coach or waking one up after a long storage period usually start there.

Repair labor is $260 per hour for mechanical and systems work. Parts carry 100 percent markup at or under $100 and 35 percent above $100. California charges 7.75 percent sales tax on parts and materials and does not tax labor. Any authorized job above $2,000 takes a 50 percent deposit before parts are ordered. A common example: 3 hours of repair labor at $260 is $780, a $310 control board at 35 percent is $418.50, tax on the part is $32.43, and the invoice is $1,230.93.

• RV systems assessment: $150, credited against an authorized repair
• Diagnostic labor: $285 per hour, first hour credited against an authorized repair
• Mechanical and systems labor: $260 per hour
• Parts: 100 percent markup at or under $100, 35 percent above $100
• Sales tax: 7.75 percent on parts and materials, none on labor
• Deposit: 50 percent on any authorized job above $2,000

License ARD00288521 and What California Requires

OCRV Center is a registered automotive repair dealer, license ARD00288521, and we hold EPA ID CAL000367879 for the hazardous waste our processes generate. Registration is not decoration. It puts a set of specific obligations on us and it gives you a specific place to complain if we fail them. Any shop working on your RV in this state should be able to give you that number without hesitating, and you should be able to look it up before you leave a deposit.

The first obligation is a written estimate before work begins, showing parts and labor. You sign it. If the job turns out to need more than the estimate covers, we stop and get your authorization for the additional amount before we continue. That call happens more often on RVs than on cars, because water damage and corrosion hide behind panels. Nobody enjoys the phone call. Everybody prefers it to an invoice that is 40 percent higher than the number they agreed to.

The invoice has to itemize what was done, list parts and whether they were new, used, or rebuilt, and separate labor from parts. You can ask for your replaced parts back, and we will set them aside if you tell us before the work starts. Keep the invoice. It is the document that matters when you sell the coach, when an insurer asks what was repaired, and when a component fails again and we need to know exactly what went in.