How to check Onan MDL4 safety shutoffs

[pmurphy]

I have a 1987 Onan MDL4 generator that I've been trying to test the shutdowns on it. Specifically the low oil pressure, high coolant temp, high exhaust temp shutdowns. I was only able to find a 12V wiring schematic (my generator is 32V) which seems to show each of these sensors as normally open connections. It looks like when they are triggered, the circuit is closed and a connection is made to ground, popping out the fault shutdown button.
I wanted to test to make sure I that was how they worked so I took a wire lead, put it on the each of the sensors and touched to ground. Nothing happened. I was expecting that to shut it down. What am I missing?

 

[whoover]

I had a mdje, the sensors were wired in series and completed a circuit to the power to the fuel solenoid. When one sensor would open it would break the circuit and shut down. Pulling a wire off any sensor while running should shut it down.

 

[rwaldrop13]

I posted the MD service manual under resources, have you looked there?

 

[pmurphy]

Rob- I have not. Didn't know it was available. I'll check it out.
Thanks

 

[pmurphy]

Well, after digging through the service manual I could not find the solution. I'm trying to figure out how to test my shutdowns somehow. I have zero knowledge as to how they work. Maybe someone can spoon feed me. I'm guessing (but haven't tried) that the pop out Fault Reset button can be manually popped out while the generator is running and it should shut down the generator by shutting off the fuel supply. Can someone confirm that before I try it and mess something up.
Then I'd like to trick the circuit somehow so that I can confirm the Fault Reset button will pop out when a sensor activates. Does anyone know how to do that?
I've added my wiring diagram hoping someone might be able to conclude which sensors might be normally open or normally closed. I can trace the wires only to when they disappear into the control box. On the back of the Fault Reset button I can see 3 wires going into it (two of which look to be the same size and type going that goes to the various sensors and one that is a bit thinner).

 

[SKYCHENEY]

According to the first Onan diagram, oil pressure is normally closed and all others are normally open.

 

[Pascal]

On these Onans, the fault breaker indicates the shut down was caused by a sensor and it will not restart unless the breaker is reset.

If the gen shuts for an reason like a fuel or governor issue the breaker will not trip

We re in the Exumas and one of the two 47kw on the boat I run has shut down three times in the last couple of weeks without tripping the fault breaker which tells me it s a fueling issue
So if yours shut down without tripping the fault breaker, don’t bother with the safety switches.

 

[pmurphy]

On these Onans, the fault breaker indicates the shut down was caused by a sensor and it will not restart unless the breaker is reset.

If the gen shuts for an reason like a fuel or governor issue the breaker will not trip

We re in the Exumas and one of the two 47kw on the boat I run has shut down three times in the last couple of weeks without tripping the fault breaker which tells me it s a fueling issue
So if yours shut down without tripping the fault breaker, don’t bother with the safety switches.

Pascal-
Mine is not shutting down. It's running fine after a lot of work to get it up to snuff. I now want to check the safety shutdowns to be sure they work. Is there any way to trick the system (like grounding out a wire, which I tried without success) to check to see if they work?

 

[SKYCHENEY]

I believe that if they work, it runs. If they fail, it shuts down.
What I mean is that if you could bypass or ground one out to test, it wouldn't be testing the switch itself, but the wiring circuit which is obviously okay or it wouldn't be running.
The only way to test the switch is to bring each one into a fault or tripping condition, ie heating up the over temp switch to get it to close.

 

[Pascal]

Pascal-
Mine is not shutting down. It's running fine after a lot of work to get it up to snuff. I now want to check the safety shutdowns to be sure they work. Is there any way to trick the system (like grounding out a wire, which I tried without success) to check to see if they

Basically if a switch goes bad, it will shut down the generator. The system is designed so That a failing switch will not damage the generator by keeping it running thru low pressure, flow or high temp.

Some switches will shut the generator down if the wire is grounded. Others will shut it down if the wire is disconnected.