Onboard and portable

RV generator repair in Pahrump

A generator is the one thing on your rig you only need where there is no power. Which is exactly where it will not start. That is not bad luck, it is the shape of the problem: it sat unused for months precisely because you were plugged in, and then the first time you needed it, you were forty miles from pavement asking a machine asleep since spring to wake on demand.

The number one cause is disuse, not wear

Most dead RV generators are not worn out. They are stale. This is the most useful thing to understand about them, because it changes what you do.

Gasoline goes bad. Not in years, in months. The light ends evaporate and what is left oxidizes into gum and varnish, and heat accelerates all of it. A generator that ran fine in October and sat all winter has a carburetor full of a substance that used to be fuel. Those passages are the diameter of a pin, and it does not take much varnish to close one. The symptom is a generator that cranks strongly and never fires, or fires and dies, or runs rough and will not take load. Ethanol makes it worse, because it pulls water out of the air and separates out at the bottom of the tank, where the fuel pickup is.

The exercise rule

Run the generator under load for half an hour, once a month. That is the single best thing an RV owner can do for a generator, and it is free.

Under load is the part people skip. Idling with nothing plugged in for five minutes does not do the job: it does not get hot enough to burn off moisture and carbon, it does not move enough fresh fuel through the carburetor, and on a diesel it leaves things worse. Turn on the air conditioner. Make it work. Half an hour of real load, monthly, and most of the calls on this page never happen.

If your rig sits for the summer, either exercise it or treat the fuel, shut the fuel off, and let it run the bowl dry. One or the other. Doing neither is how a mechanically perfect generator with 200 hours turns into a service call in October.

What actually fails

A technician working a dead generator runs an old, boring, reliable process: does it have fuel, spark, and compression, and is something telling it not to run. The answers cluster.

Fuel and the carburetor

The big one, for the reasons above. Stale fuel, a gummed carburetor, a clogged filter, a failed fuel pump, or a pickup that cannot reach because the tank is low. That last one catches people constantly: on most motorhomes the onboard generator draws from the chassis tank, but its pickup tube stops around a quarter so you cannot strand yourself. Under a quarter, the generator quits and the engine does not. People conclude the generator is broken. It is protecting them.

Spark

Plugs, and they are cheap. A gas generator run a lot fouls plugs, and one run on stale fuel fouls them faster. Coils and ignition modules fail less often, and heat is not their friend.

The oil level shutoff, which fools everybody

Nearly every RV generator has a low-oil-pressure switch that kills the unit rather than let it destroy itself. When it trips, the generator cranks normally, maybe fires for a second, then dies. No noise, no smoke, no hint that oil is the issue. It looks exactly like a dead generator.

Check the oil first. Always. Free, two minutes, and a real fraction of the "my generator is dead" calls out here. Nobody checks a generator's dipstick as often as the truck's. If it is low, top it and try again. If that fixes it you saved a trip fee, and you still want to know why it was low.

Brushes, the control board, and the rest

On a brushed unit the brushes are a wear item, and they eventually stop making contact, which gives you a generator that runs perfectly and produces no power. Engine fine, no electricity: a confusing symptom worth naming. The control board is the other one. It manages start, run, and shutdown, and it is a circuit board bolted to a hot, vibrating engine, which is not a kind place to live. Boards fail, and heat here shortens them.

Gas, diesel, and propane

Gasoline units are the most common in motorhomes and the most prone to everything on this page, because gasoline goes stale fastest.

Diesel generators live in diesel pushers, sharing the chassis tank. Diesel keeps better but brings its own list: microbial growth if water gets in, injectors and lift pumps as the expensive failures, and wet-stacking if it is idled for years with no load. The load rule matters more on a diesel, not less.

Propane generators are the clean ones. LP does not go stale, which removes the biggest cause of failure at a stroke, and they start after long storage far more reliably than gas. The trade is less power for the same size, and you are burning propane you might rather put in the fridge and water heater. If yours will not start, the diagnosis skews toward the regulator, the LP solenoid, and the ignition rather than the fuel.

Heat and altitude both derate a generator

This is the answer to a real and very common complaint: the generator ran two air conditioners in Oregon and cannot run one here, and nothing broke.

An engine makes power by burning fuel with oxygen, and what it gets is a volume of air. Hot air is thinner, so a given lungful holds less oxygen. Altitude does the same. Both cut the power an engine makes, and both are in play here. Industry rules of thumb put the loss at roughly 3 percent per 1,000 feet of elevation and about 1 percent for every 10 degrees over standard temperature. Pahrump sits at about 2,700 feet. Run that at 115 degrees and you are down a meaningful chunk of the nameplate rating before anything is wrong.

Now put that against the load. An RV air conditioner needs a big surge to start its compressor, several times what it draws once running. So: a generator making less than its badge says, on the hottest day of the year, asked for its hardest single moment, by an AC working harder because it is 115 out. That is why the AC starts fine in the morning and trips the generator at 4pm. The generator is not broken. It is at the edge of its envelope and the envelope shrank.

What helps: a soft start device on the air conditioner, which cuts the startup surge substantially and is the standard fix for exactly this; shedding other loads before starting the AC; and being realistic about which unit runs. Dropping into Death Valley is the extreme case, and a rig that manages two ACs at home may manage one down there. Worth planning around rather than discovering.

What the wattage number really means

Generators list two numbers and only one is honest for planning. Peak or surge wattage is what the unit makes for a few seconds. Running wattage is what it sustains, and it is the smaller number and the one that matters. Size against running watts, subtract for heat and altitude, then check your surge headroom covers the AC compressor kicking in. Most people who think their generator is undersized sized it against the peak number.

Portable versus onboard

Onboard generators are mounted in a compartment, plumbed to the rig's fuel, wired into the transfer switch, and started from a panel inside. Onan is what sits in most motorhomes, and the technicians we refer see them constantly, along with the Generac, Champion, Honda, and Yamaha units covering the rest. They are convenient and easy to ignore for a year at a time, which is why they are most of these calls. A technician services one in place: a generator in a bay under a fifth wheel is not going to a shop without the fifth wheel going too.

Portables sit outside and plug in. Simpler, exercised more because you handle them, and when one will not start you can put it in a truck. A portable is often the cheaper answer for occasional use, and if your onboard unit is old enough that the repair approaches the cost of a portable, say so out loud rather than authorizing the repair by reflex.

One boundary either way. An onboard RV generator is house work and squarely what a mobile RV technician does. The motorhome's engine is not: that is a truck shop, even though the two share a tank and sit ten feet apart. If a technician tells you your generator problem is actually a chassis problem, they are not passing the buck.

What it costs

Generator work has no single honest range, because the same symptom covers a carburetor clean and a control board. What is grounded is the structure of the bill: a trip fee of $75 to $150 covering roughly the first 30 miles, plus labor at $125 to $175 per hour with a one hour minimum, plus parts. A fuel-system service is generally a couple of hours of labor and a small parts bill. A board or a rewind is parts-driven and worth a real quote. The cost page covers those two numbers.