RV Generator Repair for San Clemente Owners

Ask any technician who has pulled a hundred Onan units and you will get the same answer: the generators that arrive in the worst condition have the fewest hours on them. A unit with 1,800 hours that gets exercised monthly is usually a service item. A unit with 220 hours that has sat in a storage lot for four seasons is usually a carburetor rebuild, a fuel system flush, a set of plugs, a decarbon and often a control board.

Gasoline is the main culprit. Modern pump fuel with ethanol begins to separate and oxidize within a few months. In a carbureted Onan the bowl sits at the lowest point of the system, so the residue concentrates exactly where the main jet and the emulsion tube live. Those passages are measured in thousandths of an inch. It does not take much varnish to close them.

Diesel units fail differently but no better. Algae and water in the tank plug filters, injectors gum up from sitting with stale fuel, and the lift pump loses prime. On the Quiet Diesel platform the fuel pump and the injector pump both dislike long dry periods. The remedy in both cases is exercise, not repair.

The most common thing we are told at intake is that the generator starts and runs fine, but the air conditioners will not come on. Those two statements are not in conflict. A generator can idle happily with no load and still be incapable of supporting 30 amps. Starting proves the fuel and ignition systems function at the lightest possible demand. It proves nothing about output capacity, voltage regulation or frequency stability.

Load testing is the actual test. We connect a resistive load bank and step the unit from zero to full rated output, watching voltage, frequency and how the governor recovers between steps. A healthy 5.5 kilowatt unit holds close to 120V and 60 hertz through the whole range. A worn unit sags on the step, hunts, or drops frequency low enough that air conditioner compressors will not start and control boards begin to fault.

Load testing also separates generator faults from coach faults, which is the argument owners most often lose money on. If the generator produces clean rated output at the terminals and the coach still has nothing, the fault is in the transfer switch or the distribution panel, not in the generator. That is a very different and usually much cheaper repair.

On gas units the sequence from tank to combustion chamber has four points where things go wrong. The fuel pickup tube inside the coach tank sits above the bottom by design so the generator cannot run the vehicle out of fuel, which is why a generator quits at a quarter tank while the engine keeps going. The fuel pump loses pressure or its check valve leaks down. The filter clogs. The carburetor bowl varnishes.

We work that chain in order rather than starting with a carburetor. Pressure gets measured at the pump outlet. The filter comes out and gets inspected for debris and water. Only then does the carburetor come off for a full rebuild: bowl, float, needle and seat, main jet, emulsion tube and idle circuit cleaned in an ultrasonic bath, not sprayed and reassembled. A sprayed carburetor is a repeat visit.

Diesel units get their own sequence. Filters and water separator first, then lift pump prime and pressure, then injector spray pattern. On a Quiet Diesel a rough running unit that smokes and lacks power at load is usually injectors or a fuel supply restriction, and it is worth diagnosing properly before anyone opens the injection pump.

Repeated short runs at almost no load are the standard use pattern for an RV generator, and it is the worst possible pattern for combustion. The chamber never reaches full operating temperature, so carbon accumulates on the piston crown, the valve faces and the seats. Eventually a valve does not seat, compression drops on that cylinder and the unit becomes hard to start, runs rough and will not carry load. Decarboning and a valve adjustment restores it if it is caught in time.

The exhaust system deserves more attention than it gets, because it is a safety item rather than a performance item. Onan exhaust tubing corrodes at the flex section and at the muffler seam, and a leak inside the enclosure or under the coach floor puts carbon monoxide where people sleep. We pressure check the system and inspect the tailpipe termination position on every generator that comes through, whatever the complaint was.

The sound enclosure and its mounting matter too. Missing or hardened isolation mounts transmit vibration into the coach structure and crack exhaust joints. Damaged acoustic foam falls onto hot surfaces. Missing enclosure panels change the cooling airflow path and let the unit overheat and shut down on a hot day at the Talega storage lot.

Diesel pushers and many high end gas coaches mount the generator on a slide out tray so the unit can be pulled into the open for service. When the tray works, a service that would take six hours takes two. When the tray is seized, corroded or bent, the generator has to come out through a compartment opening that was never designed for it, and the labor doubles.

Trays fail predictably. The slide rails and rollers corrode, particularly on coastal stored coaches. The locking pins bend after being driven with the tray partly out. The power tray motor and its harness sit in the wettest part of the coach and fail on a road that gets washed with salt spray. We service the tray as part of any major generator job, because a generator you cannot reach is a generator that will not get maintained.

Mounting hardware is the other half of this. Generator mounting bolts back out over time from vibration, and once one is loose the rest follow quickly. We check torque on every mount at service, and on units that have been running loose we inspect the tray frame and the coach structure underneath for cracked welds.

Automatic generator start is a convenience feature that gets blamed for a lot of faults it did not cause. The AGS controller watches house battery voltage, interior temperature or a schedule, and it starts the generator when a threshold is crossed. It also refuses to start the generator for perfectly good reasons: low house battery voltage below the crank threshold, a fault stored in the generator control board, an open shore power sense, or the front panel switch left in a state the controller cannot override.

We diagnose AGS as a communication problem first. The controller, the generator control board and the inverter or energy management panel all have to agree. Version mismatches between a replacement generator board and an older AGS module are common on coaches that have had a board replaced by someone else. Reading fault codes off the generator itself, not the AGS display, is where that gets sorted out.

Altitude matters if you take the coach east into the Sierras or up toward Big Bear. Carbureted gas generators lose roughly three percent of output per thousand feet of elevation, and above about 5,000 feet a unit that carries two air conditioners at sea level will not. High altitude jetting corrects the mixture, but it must be reversed for sea level operation. If you spend most of your season along the coast, jetting for altitude is usually the wrong trade.

Body and paint labor is posted at $210 per hour. Mechanical and electrical is $260 per hour. Diagnostics run $285 per hour with a one hour minimum that is credited back against an authorized repair. Ranges below reflect jobs we have actually completed.