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Old 02-22-2018, 08:18 AM   #1
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Onan Generator 7500 Diesel Wont Start by Switches

Hi,

We Own 1999 Airstream Class A 37 ft on Freightliner Chassis, Cat Diesel Pusher
Oman 7500 Diesel


A little history, bought Rv private sale 7/17, its in great shape. A while ago had problem with generator
starting on its own. Regardless, if it was plugged into shore line or just sitting it would
just try to start on its own. I read an old post where others had this issue. I found main harness plug on
passenger side generator was little corroded so I cleaned it. Problem seemed to be solved for week or so.
Keep in mind, I test run earthing
weekly because we live here in Fl where humidity is high.

Yesterday, it didnít matter what switch I tried inside the coach or on the gen. itself. The gen. would not turn over to start.
It would click and preheat, but wouldnít turn over, so I figured it probably had a ground problem. The batteries, 4 coach
and 2 for Cat motor are 5 yrs old. I cleaned all post, checked water levels and I test loaded them. All the batteries are fine,
11 -12 V under heavy draw for 15-20 seconds and recover quickly to 12.5 -13+ V.

When I wiggled the engine gen. (up & dwn like to start) it tried to turn over, but now it wonít do anything.

Has anyone dealt w/ this before and what did you find ?

Could I have a bad solenoid or relay somewhere.

Donít claim to be tech or mechanic, but I can do more than the average

Any help out there?

Mike
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Old 02-22-2018, 08:41 AM   #2
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Try emergency start and Gen start at same time. Check ground, batteries to coach. Check ground to Gen. Check Hot to Gen from batteries at Gen and at batteriers. Now if still no start time to start looking at Gen.

LEN
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Old 02-22-2018, 08:42 AM   #3
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The Start switch does have to be held down for several seconds sometimes longer for the preheat when it's cold outside.
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Old 02-22-2018, 02:28 PM   #4
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Has to be ground issue. Walked out today & just tried it. Started inside coach, both switches started generator. Went outside checked switch mounted on gen. Guess what it also started. What the heck. It must be a ground.

Let me ask you this guys. Is there a reset safety switch that went into safety mode yesterday & it just reset overtime. ????
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Old 02-22-2018, 02:32 PM   #5
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Quote:
Originally Posted by Edsel View Post
Has to be ground issue. Walked out today & just tried it. Started inside coach, both switches started generator. Went outside checked switch mounted on gen. Guess what it also started. What the heck. It must be a ground.

Let me ask you this guys. Is there a reset safety switch that went into safety mode yesterday & it just reset overtime. ????
We have had the 5500, 7500, and now 8000 and are not aware of a reset switch affecting the starting on an Onan.
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Old 02-22-2018, 03:31 PM   #6
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Hi Mike! Welcome to IRV2! We're sure glad you joined the gang!

I haven't encountered that problem before so can't be of any help! Keep her between the ditches!

Good luck, happy trails, and God bless!
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Old 02-22-2018, 03:51 PM   #7
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I would be suspect at the generator start solenoid. All th start switches do no more that activate the solenoid to engage the positive line to the starter. I would go to the solenoid and check the connection there. Solenoids go bad slowly understanding that all that is happening is you are integising a magnet that makes the contact between the in coming large 12v wire to the large 12v wire going to the starter.
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Old 02-22-2018, 05:13 PM   #8
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Yeah after I cleaned battery terminals today, on back gen. I let gen run for hr. everything seemed good. Walked away from RV within 5 min it tried to start again. It Did it once. Where is the solenoid
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Old 02-23-2018, 07:11 AM   #9
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Here is a link for the service manual. It may help you.

http://www.twinslan.net/~n0nas/manua...0(06-2010).pdf
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Old 02-24-2018, 04:39 AM   #10
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Thx

Yesterday, I was doing more maintenance, cleaning grounds checking wires and everything tested ok. No issues w/it trying to start on its own. At approx 6 pm I was walking away from Rv & gen tried to start once.. Very weird.

From what I reading the solenoid is like a lot of cars,mounted right on starter
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