Onan Generator Runs But No AC Output (This Is How To Solve)

Onan Generator No AC Output

Sometimes it can happen that your Onan generator is working perfectly, you can hear it droning in the background, but that you do not have any AC power in your RV.

If you don’t have much experience with the maintenance and repair of electric generators, this situation could be very confusing and alarming.

Fortunately, it is not as scary as it seems, and as long as your generator is humming, everything is OK with it.

So, why your Onan generator runs but no AC output? If your RV generator is running but not generating air conditioner output, you need to check the following steps, including:

–           Step #1: Check whether the generator is plugged in

–           Step #2: Check the generator’s alternator

–           Step #3 Check the fuses

–           Step #4: Check the generator transfer switch

–           Step #5: Check wires

–           Step #6: Check appliances for shorting

Why Onan Generator Can Run Without Power In RV?

The simple answer is because everything is fine with your Onan generator.

Ut, that doesn’t mean that there aren’t potential issues with the rest of your RV, just that there is no need to worry whether the most expensive part of it is faulty.

The situation that your Onan generator is running but there is no power in the RV can happen for two general reasons, either generator’s alternator is faulty or there is some interruption of the flow of electricity from the generator to your appliances.

Neither of these two can make the generator’s engine run out of the specs, so there is no real need to shut itself down.

So let’s get on how to diagnose what is the cause of this situation, and how to go about fixing it.

Read also: RV Generator Runs But No Power (Do This Now!)

How To Fix The Lack Of Output for Your AC

When you are away from the shore power, your generator is the sole reliable source of power you have.

Because of that, it is important that it functions properly.

If the generator is running but you don’t have air conditioner output, you may be alarmed that the generator is malfunctioning.

But, you can rest assured that your Onan generator is perfectly fine, so let’s get on with how to find what is the actual cause of this situation.

Onan Generator No AC Output: Troubleshooting the problem

Before you can fix any problem, you will need to find what is the exact cause of it.

And that means troubleshooting the problem.

One of the funny things about this type of situation is that some of the causes you can identify only by attempting their fixes, and as I continue with this article you will find out that the easiest issue is actually embarrassingly simple to fix, and you will laugh at yourself.

So, let’s get on with it.

Step #1: Check whether the generator is plugged in

While most of the newer RVs have an automatic transfer switch that automatically switches the power source your appliances are using, some older ones do not have it.

Instead, the generator needs to be plugged in by hand with the same connector you use to connect to the shore power.

In case that you have the manual for your RV, it will help you to locate where the Onan generator’s cord and receptacle are, but if you don’t have the manual it should be on the outside of the RV, usually not more than 3 feet from the generator.

“You will need to open the hatch and check whether the generator is connected to the electrical system of the rest of the RV.”

And, yes, it is super embarrassing if you forget to hook up the generator while expecting it to provide the power to your appliances.

If this doesn’t help, or your RV has an automatic transfer switch, you should continue troubleshooting the problem.

Step #2: Check the generator’s alternator

Many Onan generators have an alternator, and while checking it may sound like some very complicated procedure, in reality, all you have to do is open the access hatch to your generator.

Onan generators have an indicator light on the STOP/PRIME button, which is, depending on the model, either in the lower right corner or upper left corner of your generator.

In a situation when the generator is working but there is no power in the RV, it will either be continuously on or blink rapidly.

If it’s blinking, then the generator engine’s alternator is busted and you will need to repair or replace it.

One of the most common causes of a dead alternator is blown diodes, which can be repaired very easily in practically any car repair shop, but you should consult your dealership whether it can void the warranty if you still have it for the generator.

If the indicator is continually glowing, the alternator is fine, and you should proceed with the next step.

Step #3: Check the fuses

Both your Onan generator and the RV have circuit breakers that protect them from surges of too high current, and you should check whether some of them are tripped.

Because you are already standing next to the generator, you should check its breakers first.

But before you start checking them, you should turn off your generator.

To access them you will need to remove the front panel of your generator, and depending on the model they will be either next to the START/STOP buttons, or on the side of the control module.

They either look similar to your house circuit breakers with a leaver or have a big red ON/OFF switch.

If one of these two breakers is tripped you should reset it and start the generator.

“In case that a surge of power or turning on too many appliances have tripped this breaker you will now be fine, as the power will return to RV.”

But, if the breaker was tripped by a short circuit, it will trip as soon as you start the generator, so you can move to Step #6 and how to identify which appliance is problematic.

Onan Generator Fuse Location

The fuses and the actual radiator cap on Onan generator are usually located inside a small panel near the circuit breaker and start switch. The panel is held closed with a screw.

If breakers were not tripped on the generator, they maybe are in the RV’s main fuse box, so you should check them too.

If none of the breakers is tripped, you should turn off the generator and slightly press them one at a time with your finger.

There are chances that one of them has slipped, so no reasons not to check for it while you have RV’s fuse box open.

If the breaker has slipped, it will have a bit of a give and wiggle about.

Onan 4000 Generator Fuse Location

Cummins Onan RV QG 5500 Fuse Breaker replacement >> Check out the video below:

Step #4: Check the generator transfer switch

Most of the newer RVs have an automatic transfer switch that automatically switches power to the generator when it is turned on.

To diagnose whether it is faulty is helpful if you have access to shore power.

If your RV systems come to life when you hook up to shore power, the transfer switch is broken and needs to be replaced in the shop.

In case that power doesn’t come on, chances are that the wires behind it have come off, and need to be reattached.

Step #5: Check wires

To make sure that it is the transfer switch broken, you should continue troubleshooting by inspecting all of the power leads in the RV’s fuse box.

Simply check whether some is disconnected and tighten if needs be.

If everything is OK, you should go back to the generator and check there too.

If all wires are properly seated and connected, it would be a good thing if you have a multimeter, to check it more thoroughly.

At the generator, you will need to check the voltage at the output terminal block TB2, so you will need now to turn on the generator.

Be careful that you will be working with live wires, so if you are not skilled enough you should not attempt it yourself, but instead skip to the next step.

If you are skilled enough, you need to measure the voltage across TB2-1 and TB2-3, and across TB2-2 and TB2-4 terminals.

There should be a voltage of around 120V, in which case there is some problem with the AC harness leading to the RV and it needs to be replaced in the shop.

“If there is no voltage, you need to remove the top housing panel of your Onan generator and check whether the AC harness is properly connected to TB2 and TB3 terminal blocks, and the breakers.”

If something is not properly secured, turn off the generator and reconnect it.

Otherwise, you should measure the voltage across TB3-1 and TB3-2.

If you measure 120 volts, the AC harness is faulty and it needs to be replaced in the shop.

But, if there is no voltage the control assembly is broken and needs to be replaced at the shop.

To be 100% certain that it is the control assembly, you should again power off the generator and check with a multimeter for continuity on both breakers across their terminals when they are in the ON position.

If there is no continuity on one of them, this breaker is faulty and you should replace it.

Step #6: Check appliances for shorting

In case that whenever you turn on the generator, a breaker gets tripped, problem is that one of your appliances is shorting.

Finding which one is actually very simple, all you need to do is to unplug all of the appliances, turn on the generator, and plug back in and turn on appliances one at a time.

Once you turn on the problematic appliance, it will trip the breaker and lose power.

The solution for this is to fix whatever may be the reason why that appliance is shorting.

But if none of the appliances is tripping the breakers, problem is that all of them together are overloading your Onan generator.

And to make sure of that, you should start powering them one by one, and before you power all of them r once you power the last one a breaker will be tripped.

This situation can happen for two reasons, either your generator is too small to power all of the appliances you wish to have on at the same time.

Or you are at a too high altitude for your generator to provide the maximum rated power output.

Onan generators, especially the models that are running on the propane, are sensitive to altitudes above 5,000 feet and can lose up to 15% of maximum power at altitudes above 9,000 feet.

Onan RV Generator runs but no electric




Mike Gilmour

Hi, I'm Mike, co-founder, and editor of RV and Playa. My passion is traveling (with my RV) and enjoying the day at the beach (Playa)! Well, I originally created this blog as a way to share what I've learned by experimenting with the RV lifestyle, and I want to help others develop in life through new skills and opportunities.

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