Onan Problems

1976 Palm Beach

TZE166V100710

Onan Problems

Onan Generator Doesn't Generate

PROBLEM:

In August 2006 my neighbor came to me with a problem. His 4,000 watt Onan wouldn't power his roof air conditioner. It would power everything else up to almost the rated capacity of the generator. We plugged all combinations of heaters, lights and other loads and they worked just fine. If he turned on the AC fan only it worked. If he turned on the AC compressor everything would stop. Using a volt meter we noticed that voltage would go to almost zero. As soon as the AC was turned off everything that was running with the AC would start again. After a series of tests I wrote the GMC mail list for help. Those that replied suggested that either we had a bad air conditioner or that there was a problem in the wiring someplace.

SOLUTION:

I found a loose/corroded neutral wire connection in a junction box located in the Onan compartment. I cleaned it up and made sure the wire nut was tight. The problem went away. I didn't know that there was a junction box located in the back of the Onan compartment in a '73. I don't think my '76 has one there.

Read the following text for more information on what we did:

I sent the following email to the GMCNet to see if anyone could shed some light on how to solve our problem:

-----Part of the Original Message-----
From: RJW
Sent: Wednesday, August 16, 2006 6:29 PM
Subject: [gmclist] MYSTERY: ONAN genset works for most things but won't run roof air conditioner

Now my neighbor has a problem with his GMC. He is 86 and is the original owner of a '73 23' Canyon Lands. He is one of the reasons I bought a GMC in the first place. Even though he is 86, he still feels good and wants to start driving his GMC again. It's been a few years since he drove it anywhere because he and his wife have been members of a travel club here in Michigan and have traveled with them extensively for the past 10 years leaving them little time for GMC travel.

He has a problem with his GMC I can't figure out. For some reason he can't run his roof air conditioner with his 4,000 watt Onan. It works fine with 20 amp shore power. Listed below is a summary of the things we did to try and figure out the cause of the problem:

SHORE POWER: A/C unit runs properly (both fan and compressor)
ONAN POWER: A/C blower works fine, but as soon as he tries to start the compressor the voltage, which was ~130, goes down to close to zero and everything that was running stops. As soon as the AC is turned off, the voltage goes back to (~130)and whatever else was on before starts running again.
ONAN POWER: We can put around a 3,000 watt load on the 4,000 watt generator with a space heater, water heater, hair dryer and converter. The voltage goes down to ~120 but everything runs except the A/C.
For more tests we brought my GMC over and put it next to his. We plugged his GMC power cord into my Onan receptacle. When we did that everything in his coach works fine, including the A/C from my Onan.
We then plugged my GMC power cord into his Onan receptacle and the same things happen in my coach (items 2 and 3) as in his.
I couldn't find any connectors in the AC power line from the Onan circuit breaker to the coach breaker box. The connectors in the Onan receptacle and by the Onan's breaker seem tight and secure. We measure ~130 volts at both sides of the Onan's breaker with it running until turning on the A/C and compressor causes the reading to go down to close to zero.
We now are pretty sure that problem is with his Onan and not with the coach wiring or the A/C unit.
So we replaced the Bridge Rectifier even though I figure a BR failure would result in no AC power at all. I had never replaced a BR before so this was a chance for me to learn how to replace a BR at home rather than on the road. After replacement we find that the problem persists. As it turned out someone previously had replaced the BR because there was no socket as in the OEM setup.

I got a number of responses, most were to check the air conditioner:

I would check the capacitors and relays on the AC unit. The land line could carry the load perhaps better than the Onan.

Hardie

Listen, our coaches are getting older, this means that original parts are reaching the end of their reliable life. If you replace the caps on the AC what's to keep the next old part down the line from giving up the ghost? Here you spent how many hours fiddling with the unit, going to find obscure parts and all you end up with is the same old roof AC that could stop any minute.

Don't dig a hole and bury the old roof AC, it has stuff in it that the EPA would probably frown on being under your petunias, that's why I toss them off the roof, if I'm lucky, the gas will burst out saving me the job of doing it myself-- its also a great tension release to heave that boat anchor off the side of the coach and have it crash and burn on the pavement, it gave you it's last measure of pleasure!

Jim

I must not have made it clear in my email that we had pretty well eliminated the air conditioner as the problem. There were a few that suggested a wiring problem in the Onan or in the line running to the Onan receptacle.

While I would agree that if this was a shorting condition, it would be critical and I would have been as excited as you seem to be. I think maybe you missed some of the thread. The generator works OK, if not perfect, under other loads and the AC works fine on every source except that generator. The various diagnostic procedures have pretty well isolated this to issue to the Onan and not the AC, Zero volts can be caused by a lack of connection as well as a short and that is much more likely with a generator and AC unit that work under some circumstances, but not when connected together.
Ken

Check the brushes and the wiring to the brush-holders. I have had that problem and the brushes where stuck in the holders. The springs did not push them onto the commutator rings hard enough. I am not sure but I think the last thread had something about a bad wire going to the brush holder.
Dave

It must be a loose connection that has a high resistance under load. Check the brush wires and you also might want to refer to this that I posted over 5 years ago.

The manual shows that if a high low voltage occurs when there is no load at 1800 rpm but the loaded condition has the proper voltage it is probably a bad "compounding reactor". So, I started working on the Onan with this as the premise. I quickly discovered that I would have to remove the whole brush end of the Onan to get at this part so I decided to see if I could test it while in place.

It has a lead going to the bridge rectifier which is easy to get at by just pulling off the plastic cover under the lower rear part of the brush housing. While under the Onan I accidentally discovered that another lead going to the rectifier was very loose at a connection and would not hold together. There are two male/female spade connectors going from the field windings to the + and - terminals of the rectifier. Each set is in its own approximately 2" plastic insulating tube. They are made of brass and I found that there was very poor contact as the brass female connector had lost its tension. I attempted to squeeze it with some needle nose pliers and it immediately cracked. I then soldered in a new steel female connector, coated it with dielectric grease and plugged in back to the male connector in the tube. I checked the other connector and found that it also was making very poor connection and was also loose in the tube. I replaced that connector as well.

Those connectors in the plastic sleeves have caused problems with voltage for more than one GMCer.

There is also a connection in the 120 volt lines running from the Onan to the receptacle. They are probably wrapped in a wiring harness that leads into the wall to the left of the Onan. If this connection is loose it could also cause what you are experiencing.
Emery

There were several loose connections in the wiring to the bridge rectifier. I corrected them but the problem persisted. We had pretty well isolated the problem as being somewhere between the Onan and the Onan receptacle.

Neighbor standing next to his 23' Canyon Lands.

Cross feeding each other's GMC.

I didn't have to crawl around under my neighbor's GMC, we just put it on his service ramp for access to his Onan.

Onan receptacle

Bridge rectifier replaced previously by persons unknown.

View of the "plastic sleeves" and generator brushes.

We replaced this bridge rectifier with a new one but problem persisted.

Easy access to rear of neighbor's Onan.

Problem was caused by a loose and corroded neutral line in the junction box. Cleaned and tightened the connections in the junction box.

Slid the Onan back inside and neighbor was good to go.

ONAN OVER VOLTAGE PROBLEM

PROBLEM:

Around about the Fall of 1999 I was driving my GMC with my wife and parents and had the Onan running so that they could all watch TV. All of a sudden, while going about 70 on I75 in Michigan, I noticed smoke pouring out of a power strip I had up front by my seat. I had the TV plugged into it and a voltmeter. Besides the smoke, I noticed that the meter was pegged at its maximum of 150 volts. I quickly told my wife to shut down the generator. After we got home we found that the TV was OK. The power strip, which was also a surge protector, had burned out. It must have saved the TV. Later I found out that my microwave wouldn't work. Somehow the Onan put out too much voltage and fried the microwave.

SOLUTION:

The cause I discovered later was in the linkage from the carburetor throttle to the ball on the governor arm. The ball would sometimes bind up and cause the throttle to stick. The day we had our problem my wife decided to heat something up in the microwave. That caused the Onan to increase its throttle setting and it stuck. When the microwave shut down, the throttle was stuck open more than needed for the decreased electric demand. That caused the Onan to speed up way over 150 volts, thus frying the microwave and surge protector. I fixed it by buying new ball joint assembly and governor spring. Since then I've had no more runaway problems. I also installed surge protectors everywhere in my coach to protect the TV, VCR, DVD and new microwave.

Emery apparently had the same problem and he wrote it up in an email. He sent it to me as part of what to look for with my neighbor's problem that I talk about at the beginning of this page. I'm including it here because he describes how to adjust the linkage better than I could and it's something that everyone should take a look at.

This is the rest of Emery's email:

you also might want to refer to this that I posted over 5 years ago.

<<<<On the trip to Palm Desert, my Onan was not putting out much voltage when a load was applied. When I had the water heater and the coffee pot going at the same time (under 3000 watts) the voltage would drop to about 100v. I tried adjusting the carb, the governor speed and sensitivity and got the voltage to finally hold at 110v with this load. However, I didn't go back and check the no load voltage. Unfortunately, I later discovered that my no load voltage was in excess of 150 volts (thats as high as my plug in voltmeter would display) and the result was that I fried my Statpower charger when I started up the Onan the next morning.

The manual shows that if a high low voltage occurs when there is no load at 1800 rpm but the loaded condition has the proper voltage it is probably a bad "compounding reactor". So, I started working on the Onan with this as the premise. I quickly discovered that I would have to remove the whole brush end of the Onan to get at this part so I decided to see if I could test it while in place.

It has a lead going to the bridge rectifier which is easy to get at by just pulling off the plastic cover under the lower rear part of the brush housing. While under the Onan I accidentally discovered that another lead going to the rectifier was very loose at a connection and would not hold together. There are two male/female spade connectors going from the field windings to the + and - terminals of the rectifier. Each set is in its own approximately 2" plastic insulating tube. They are made of brass and I found that there was very poor contact as the brass female connector had lost its tension. I attempted to squeeze it with some needle nose pliers and it immediately cracked. I then soldered in a new steel female connector, coated it with dielectric grease and plugged in back to the male connector in the tube. I checked the other connector and found that it also was making very poor connection and was also loose in the tube. I replaced that connector as well.

I next started the Onan and found that I had much higher voltage than before. I used a mechanical tach through the front flywheel cover hole and set the no load to 1800 rpm which corresponds exactly to 126 volts. I went through the various adjustments with the carb, the governor speed and the sensitivity and was able to get 126 volts at no load but it would still drop to about 110 with 3000 watts. That's about where is used to be and I figured that I would have to live with that and just turn the water heater off when I wanted to use the microwave as we had been doing for the last few years. I then noticed the paragraph in the maintenance manual about the linkage adjustment (from the carb throttle to the ball on the governor arm).

I had never adjusted that so I decided to check it. Following the instructions, with the Onan off, I popped it off the ball joint and held the carb wide open against its stop and checked the end against the ball joint. I found the linkage to be about 1/4" too long. I rotated the end until it just fit over the ball stud. I then restarted the Onan and readjusted the carb and governor until I again had 126 volts at no load. I then started to turn on electrical equipment and found that the voltage never dropped below 120 volts. I started with the water heater, added the coffee pot, the air conditioner heat strip and even the microwave and it would still hold at 120 volts. I calculate that I had about a full load of 6000 watts on the Onan. It has never done this before in the 20+ years that I've had the GMC.

I had never thought to adjust the linkage arm before. In fact, the factory paint was still on the threads when I turned the end to shorten it. It apparently had never been set properly by the factory.

I also noticed that there are two more of the connectors in the same type sleeves on the left top of the Onan in the wires going to the fuel pump and to the solenoid. I checked these but they were tight. Apparently the heat from the engine and generator caused the lower brass field wire connectors to loose their temper and thus cause a loose connection.

I would suggest that everyone check these two connectors and the carb linkage on their Onan. There was nothing wrong with the compounding reactor. I believe that my initial problem was occurring because of intermittent contact on the field windings.

Those connectors in the plastic sleeves have caused problems with voltage for more than one GMCer.

There is also a connection in the 120 volt lines running from the Onan to the receptacle. They are probably wrapped in a wiring harness that leads into the wall to the left of the Onan. If this connection is loose it could also cause what you are experiencing.

Emery

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Page was last modified: 08/23/2006 03:38:43 PM