701a aux pump no power

[helomedic1171]

I've got a 701a that runs great. fans turn on, engine purrs, cranks up right away on a pair of motorcycle batteries.

Problem is, the aux pump doesn't turn on. I've tested the pump itself on my MEP003a 10kw, and the pump is good. I checked power at the wire coming from the harness going to the cigar-shaped EMI capacitor, and it reads 0 vdc there. So I'm not getting power to the pump. I'm trying to figure out how/where to test the float switch or if there's a way to bypass it to make the pump run, but haven't got that far yet. I've tested the master switch and I have power when the switch is in "aux/run" at position 17, and I don't have power at 17 when the unit is in "run".

Near as I can figure, I don't have power after the master switch but before the pump. there's no obvious breaks in any wires, and my next target is the float switch. Anyone have any tricks or tips on checking the float switch or why the pump isn't getting power?

 

[helomedic1171]

Checked continuity from the pump power wire to terminal "A" of the big Cannon plug at the rear of the control box, and it does have continuity. It continues to have continuity all the way to terminal 6 of block TB2 on the circuit board.on the left hand side. I can't seem to find where the circuit goes from there.

 

[Chainbreaker]

I don't have a MEP-701a but... float switches are often problematic due to sticking. I would take it out and clean it well using a solvent and then test continuity of its contacts while out. Even if it's not the problem, servicing the float switch by cleaning, working it and testing is just good periodic maintenance.

 

[Guyfang]

Have you down loaded the TM's? The schematic is needed to trouble shoot this problem. Here is a quick shot to help you get started. There is much more in the TM.

 

[helomedic1171]

I have, but the diagrams in it did not look like this. Thanks guyfang!

As for the float switch - continuity is good through pins A,B,&C when "empty". I pulled it out to check. Floats seem to slide easily up and down and actually float when in diesel. I'll clean it while I have it out though.

 

[Guyfang]

Where did you get your schematics. There should be the same one I posted in the TM forum.

 

[helomedic1171]

I'll take a look. It might be an old version that I have.

 

[helomedic1171]

Here are the TMs that I have:

TM 5-6115-640-14&P
TM 5-6115-615-34
TM 5-6115-615-12
TM 5-6115--615-24P

I think I've been working out of -34 and -14&P, not -12 so I'm going to dive into that one today.

 

[helomedic1171]

I need to check CB1 because master switch pin 17 goes there, and then I need to figure out what comes off that CB and where they go if it's good.

I'll admit, the cannon plugs confuse me. I can't reaidly figure out once a wire goes in there, where it goes next or where it pops up.

 

[Guyfang]

Best to use the schematics out of the -12 TM. A while back, I extracted all the schematics to make using them easy.

 

[helomedic1171]

Thanks for the extracted files. I saved them for later.

I've been looking at them and I get lost as to where the individual wires go once they get to a cannon plug.

When I turn the master switch to "prime/run Aux" there is a clunk as though a solenoid or relay is engaging, but the pump doesn't make any noise and is not getting power as verified with my Fluke meter. The float switch is good and has continuity, and the wiring from the big Cannon plug at the back of the control box to the fuel pump has continuity even through the float switch.

The master switch is showing power on the meter, about 23.7 vdc at present.

Shouldn't there be a relay or something in-between the master switch and the cannon plug? If so, what does it look like? Is there anything else I should check?

 

[helomedic1171]

I think I may have figured something out.

A1-TB2-9 is supposed to have 4 wires coming off it:

GND (missing)
A1-VR2-B(-) (currently connected to A1-TB2-
A2-M4(-) (correctly connected)
A1-J1-N (correctly connected)

So I should probably start by fixing the incorrect wire and the missing ground, right?

Am I even reading the diagram correctly?

 

[helomedic1171]

I got the Aux pump working. I switched the wires to their correct positions and it works great now.

Now I just need to figure out how to wire it to run a camper.

Thanks for the help.