MEP-802A Popping CB1 as Soon as the Unit is Switched to Pump/Prime

[Blockwarden]

Greetings,

I am new to posting here, but have read a lot of post from this forum over the years, lots of great information!!

I have a MEP-802A that was working fine. During a recent power outage I brought it online and it was supplying power as it normally does up until the lights went out. I went outside to find the generator totally shut down and it took me a few minutes of messing about in the dark to discover that CB1 had popped, I reset it and closed the panel and tried again. As soon as I switched it to "Prime/Pump" the breaker immediately popped again.

I read the prior thread on this, but this seems different since the breaker is popping immediately. I checked the wiring from the oil pressure sensor and all appears to be intact. I followed the schematic and found that CB1 only governs 4 components in the machine, the question is what parts to start replacing besides the circuit breaker itself?

Any advice is more than welcome as we are still in the tail end of winter and vulnerable to power outages due to wind.

 

[Scoobyshep]

Need to start isolating things, Id start with fuel pumps

 

[Ray70]

Hello and welcome. My first thought would be to unplug both fuel pumps. The primary and aux. to see if one is shorted.
As Scoobyshep mentioned.... I assume you meant the DC circuit breaker is popping??

 

[Blockwarden]

Hello and welcome. My first thought would be to unplug both fuel pumps. The primary and aux. to see if one is shorted.
As Scoobyshep mentioned.... I assume you meant the DC circuit breaker is popping??

I just went out and validated, it is CB1 right above FU1.

 

[Ray70]

You are correct. CB1 is the DC breaker.... Not CB2.
It should be controlling pretty much all of your 24V system.
I'd try disconnecting the fuel pumps first.
Maybe try disconnecting the primary pump first, since the aux. pump requires you to remove the end panel around the fuel filler.

 

[Scoobyshep]

You are correct. CB1 is the DC breaker.... Not CB2.
It should be controlling pretty much all of your 24V system.
I'd try disconnecting the fuel pumps first.
Maybe try disconnecting the primary pump first, since the aux. pump requires you to remove the end panel around the fuel filler.

That bit me too, The 00s are the other way around.

 

[Guyfang]

Normally the primary pump.

 

[Blockwarden]

I'll disconnect it tomorrow and see where it goes from there. I have a feeling that I may need to also inspect/test the wiring for rodent damage. Last time there was a problem was when mice made a nest on the main terminal block that ended up electrocuting all of them and started a small fire in the process, that was a bit more straight forward to diagnose and repair

 

[Ray70]

Very well could be a chaffed ( or chewed ) wire anywhere causing the problem.
Just have to isolate things to try to narrow it down till' you find the problem.

 

[Blockwarden]

Ok.. Sorry it has been so long, a lot of stuff going on.

I tried disconnecting the main fuel pump, breaker still pops. I took the alternate approach and disconnected the two output lines from the breaker one at a time. Wire #135A20 is causing the breaker to blow. Any chance that these are all wired the same with a standard harness/wire number pattern? The schematics inside the doors are fairly useless without wire numbers.

Thanks in advance for any insight.

 

[Scoobyshep]

They are supposed to all ve wired the same and per the schematics. But since this is reality and not fantasy, the drawings are more of guidelines

 

[Light in the Dark]

Ok.. Sorry it has been so long, a lot of stuff going on.

I tried disconnecting the main fuel pump, breaker still pops. I took the alternate approach and disconnected the two output lines from the breaker one at a time. Wire #135A20 is causing the breaker to blow. Any chance that these are all wired the same with a standard harness/wire number pattern? The schematics inside the doors are fairly useless without wire numbers.

Thanks in advance for any insight.

The schematics have the wire number and alphanumeric on them on all diagrams (see below). They only lack the two trailing numbers (which are the gauge of the wire, and irrelevant to the layout purpose of the schematics).

For example below... the wires involved with the MT4 are 112B, 112A, 159A, 158A, 109J, and 109K.

 

[kloppk]

Wire 135A20 is the +24 volt input to the circuit breaker.

 

[Blockwarden]

Wire 135A20 is the +24 volt input to the circuit breaker.

Interesting. Apparently someone wired the breaker backwards since that was attached to the "Load" terminal of the breaker and not "Line".

Guess it was bad for me to assume, I'll take the meter out and verify where power is coming from and going to.

 

[Guyfang]

This is a copy of the schematic. Its in the books and on the door. There are wire numbers on it. is the switch wired like this?

 

[Guyfang]

Perhaps you need to download this, print it out and put it in a document protector.

 

[Blockwarden]

Perhaps you need to download this, print it out and put it in a document protector.

Thank You!

 

[Blockwarden]

Ok. So I finally had a chance to revisit this.

I tried unhooking the main fuel pump and still get a breaker pop. From what the schematics say wire 136D maps to the master switch, when disconnected the breaker does not pop, but nothing works. So from what I am seeing that leaves 4 options since contacts 2,4,6,8 are all slaved together, and I am not discounting the idea of improper wiring since I already found out that CB1 was wired backwards (Line was on Load and vs. versa).

The diagram for S1 is very ambiguous since none of the numbers on the left identically match the manifest in schematics that Guyfang provided. I am far from a professional when it comes to schematics and electronics in general. I could just start unhooking them one by one to find the culprit, but that does not seem to be the smart way to do it (or maybe it is and I just don't know it).

I thought that I heard at one point that the diagnostic connector, that they never designed a tool for, can be used with a meter to isolate problems, is that true?

I really do appreciate the help so far as I slowly muddle through this.

 

[Scoobyshep]

are you sure the CB is good? It's rare but I have had it happen before. Fast and dirty test: get a fuseholder and 7.5 amp automotive fuse and jump the cb (make sure the cb is in the open position) fuse blows you have a short somewhere it doesn't blow and you have a bad cb.

 

[Light in the Dark]

You can also unplug the AUX pump, as well as the double float in the rear tank (and the rear fender switch... but thats almost NEVER the culprit). Just unplug one at a time and see if you can find the problem.

If none of those give you the AH-HA, then you need to start verifying wire numbers and positions.