mep8o2a low oil pressure shut down

[Guyfang]

From​	Wire #​	Terminal #​	Terminal #​	Wire #	From
K20-7​	102A​	A​	B​	100AZ​	TB5-10​
		1​	2​
		3​	​
K15-6​	119L​	4​	4​	119H​	TB5-2​
P4-1​	127A​	5​	6​	150D​	TB5-19​
K20-A​	102A​	7​	7​	102B​	K15-9​
J7-5​	126B​	8​	8​	126C​	J2-a​
TB5-2​	119A​	9​	​

Wire diagram for K20

 

[builmord]

Well finally the rain has cleared, now its just cold at least to me a Florida boy now living in the cold north of Virginia. I tested k20 and have 24v on terminals a & b and relay works by visual inspection. I looked hard for anything abnormal in the wiring harness and connections. everything looks good. now someone disconnected the oil pressure switch for a reason and maybe did something to the fault display as it shows no faults. where to go next is the question. the wiring diagram on the unit is difficult to follow

 

[kloppk]

Have you downloaded the -24 TM?
It has everything you'd want to know about every wire in the set.
The schematic and wiring details are in the back of the TM.

 

[builmord]

my confusion is not knowing what action each device does when energized or in the case of s1 when moved to the start or prime run position. I can follow the wires to their respective terminations but without knowing the energizing or switching that goes on in each device confuses me . s14 is a nother good example. I assume it drops out the starter among other things when engine rpm is reached

 

[Guyfang]

Have you tested the switch yet?

 

[builmord]

yes, oil pressure switch is OK both no and nc contacts work as they should

 

[builmord]

I found the diagram for s1, my mistake it was available. question #1 should I remove the K relays to test them ? #2 should I remove the battle switch to test it. #3 could a defective battle switch be the reason no fault shows up with oil pressure switch disconnected ? My fault panel works for water temperature and current overload as both of these have happened and the unit shut down and the panel showed the fault

 

[builmord]

HELP PLEASE ! on the wiring diagram I can not figure out what energizes the coil in K20. What do the upside down triangles with a letter in them stand for

 

[kloppk]

The upside down triangles indicate which pin on the diagnostic connector that signal goes to.
See Table 2-10 in the -24 TM for the diagnostic connector pinout.

 

[kloppk]

Working on tracing it out for you

 

[builmord]

thanks, my questions show how little I know about wiring diagrams

 

[Guyfang]

I found the diagram for s1, my mistake it was available. question #1 should I remove the K relays to test them ? #2 should I remove the battle switch to test it. #3 could a defective battle switch be the reason no fault shows up with oil pressure switch disconnected ? My fault panel works for water temperature and current overload as both of these have happened and the unit shut down and the panel showed the fault

In almost 30 years of fixing gen sets, I might have seen one S7 bad. Waste of time.

 

[builmord]

how does coil k20 energize ? is coil K12 feed from A2 through contacts 7 and 8 in S7

 

[kloppk]

I haven't had a chance to fully flush that out but I suspect 24 volts is supplied by the NC contacts on K12 located to the right of A2 on the schematic. Also it looks like K20 gets latched closed when the field gets flashed.
Will try to dig further when I get home later today.

Of course Guy could probably tell you off the top of his head!

 

[Guyfang]

The K20 coil, is in series with a set of normally open contacts from K15 and K16, and the LOP. Its not quite that simple, you need to look at the schematic. If Kurt can not write one up, when I get back home maybe I can.

 

[builmord]

A2 must have some switching ability as I look at the drawing and there is no closed circuit to the coils of K2 or K12. it also appears when K12 is activated through A2 it opens circuit to fuel pump and closes circuit to its coil so it no longer needs power from A2




path to either K20 or K12 coils

 

[Guyfang]

quick note. A2 has no switching function. The gen set runs just fine with no A2 in it.

 

[builmord]

this is just a question. the gen runs fine when the battle switch is turned on as well. without A2 in the circuit low oil pressure or for that matter any other fault would do nothing to stop the engine. isn't that what the battle switch does , bypasses all safeguards. please excuse my ignorance, I am learning how this system works

 

[kloppk]

Battle Short bypasses most faults. It does not bypass a Short Circuit fault.

 

[builmord]

Thank you Guyfang and Kloppk . Your help made me realize I was seeing the controll circuit power flow in the wrong direction. And yes A2 does not switch anything. What I did discover is on the far left /top of the wiring diagram there is an open contact K15 , it wasn't clear on the drawing. this is the initial step of powering up K20 that I couldn't find. K15 coil is energized by S1 terminal #7 when S1 is held in the crank position. this closes this normally open contact which power flows through to the coil of K20 intil S1 is released to the run /prime position. once energized K20 holds itself closed until a fault occurs and closes any one of the normally open contacts in parallel along with the pressure swirch and they terminate in A2. any closed contact due to a fault powers A2 #13 terminal that brings the fault power to battle short switch . hear it will stop if the battle switch is open and the gen will continue to run. if it is closed the power will energize the coil on K12. which in turn will close a set of K12 normally open contacts providing a second path of control power from terminal #3 on S1 to hold K12 energized until you manually turn S1 to the off position. it will also open the normally closed contacts cutting power to the fuel pump thus causing the engine to stop. I believe I can now trace and find why my system isn't responding to a low oil pressure fault. Thank you everyone for your help