GMC Electrical Problem

[emerystora]

>All electrical circuits in my 75 PB work fine while connected to shore power.
>But, when connected to and running the Onan, the circuit for the coach
>receptacles and the rear A/C circuit are dead - no voltage. This indicates to
>me that the problem is between the generator and the generator receptacle.
>When I read voltage at the generator receptacle, the right side reads 130
>volts and the left side reads 17 volts. The schematic in the manual shows
>just two wires from the generator to the receptacle but I think there are
>more likely to be four. If one is open or has a poor connection, it might
>explain the voltage problem. The PO replaced the original Onan and in so
>doing, removed the roll out feature. It is therefore difficult to check the
>leads from the generator but it is possible from the inside if a panel is
>removed. I will check the connection at the generator that way and the leads
>to the receptacle, but if they seem OK, could the problem be in the generator
>itself?
>
>Andy M PA

Andy - Jim Walker of Texas was coming through New Mexico in early May
and had a similar problem. He and I attacked the problem in the
local Walmart parking lot. First we thought that it might me a bad
diode set but when I put in a new one still no 120 volt in the coach.

You can check to see if there is 120 volt output by pulling the small
panel off the box with the reset button. This in in the 120 volt
output circuit. You put one lead of your volt meter to ground and
the other lead to the reset switch. You should check both sides of
the reset. If you have 120 volts on both sides then the reset button
is working and so in the generator. If 120 on only one side of the
reset switch and zero on the other side then you have a bad reset
switch or a tripped switch. Push the button to reset it and then
check the other side. You should have 120 volts on both sides. If
you have zero volts on both sides then the problem is in the Onan.
Might be diode, brushes, or something else.

If you have 120 volts on each side then go to the box where your
power cord plugs in. Check to see that you have 120 volts at the
receptacle. If not, then you probably have a problem with the two
wires (only two wires) that lead from the Onan to the receptacle.
From the reset box at the Onan, a wire goes down and out the rear
bottom corner (there are two wires only - a hot lead from the reset
box and a ground lead). From that corner of the Onan box they go
into the wall of the GMC just in front of the lower part of the Onan.
From there they go up to the receptacle that your power cord plugs
into. The power cord goes to your breaker box.

With Jim Walkers GMC we did have voltage at the reset box. We did
NOT have voltage at the receptacle. First we took apart the
receptacle. No voltage on the wires at the back. We then traced the
wires going from the Onan into the wall. We found a two connector
plug in that line near the Onan and found that it was badly corroded.
We cut out the plug and hard wired the wires together and that solved
the problem.

Don't know if this is your problem but you might want to use this
procedure to check things out.

Emery Stora
77 Kingsley
Santa Fe, NM

 

[emerystora]

>I should have made it clear that with the Onan running, the front A/C and
>other circuits work. Its just the inside receptacles and rear A/C that don't
>work.
>
>Andy M, PA

Andy - in that case your Onan must be operating properly. Since
there are just two wires coming from the Onan to the receptacle, and
the receptacle has four contacts, GM put a jumper across the left and
right hot leads at the back of the receptacle (the flat bar slots).
The Onan connects to one and the jumper connects it to the other.

Your problem is either in that receptacle or in the cord or your
breaker box. If you have voltage at both flat spade terminals at
your receptacle then it is in the cord going to the breaker box or in
the breaker box. Remove the cover from the breaker box and carefully
check the voltage at the red and black wires that go the sides of the
box. Then check the output of the main breakers and also of the
breaker that goes to the receptacles and to the rear A/C. Also check
all your white leads (ground or common) in the breaker box. Your
problem must be at one of these points.

Emery Stora
77 Kingsley
Santa Fe, NM

 

[emerystora]

>Emery,
> Its good to talk through this with you. Based on what you said and
>what I have found, because everything works on shore power, it seems that
>would rule out the cord and breaker box. Correct? If so, that leaves the
>generator leads and the receptacle as suspect. When I check voltage at the
>receptacle,(think of it as a clock), I get 130 volts reading between 12 and 3
>o'clock and 3 and 6 o'clock. Reading between 12 and 9 o'clock and between 9
>and 6 o'clock, I only get 15 or 17 volts. Since there are only two leads from
>the generator and one side of the receptacle reads 130v, it would seem the
>receptacle (the jumper?) might be the problem. I'll open that tomorrow.
>There's really no logical reason that should have faulted, but on a GMC, I
>guess anything can happen. I'll let you know. Thanks for the help.
>
>Andy M, PA
>75 PB

Andy - If the flat holes in the receptacle are at the 3 and 9 o'clock
positions, it sounds like you've got it. Mine are at the 12 and 6
o'clock positions which makes it easier to plug in the cord. I
rotated it years ago.

I agree that it can't be the cord or the breaker box or the breakers
since you say everything works on shore power. Good News -- It also
can't be the leads from the Onan to the receptacle because you've
only got a ground and a 120 volt lead (your Onan must be revving a
bit higher and putting out 130 volts) and you've proven that you have
130 volts to the receptacle. If the land line works all right, it
must be either the jumper behind the receptacle, loose wires at the
back, or the contact in the receptacle itself.

Nest step is to open the receptacle box and check things out. Best
case, loose wires. Worse case you'll have to replace the receptacle.
If you take off the front plate to get at the wires you might find
that you'll have to pull the oven to get at the box in order to hold
it so you can tighten the face plate back on. When GM made it they
just clamped it in place with the face plate on one side and the box
on the other. The box tends to push away when you try to tighten the
screws.

I'm fairly certain that you've zeroed in on the problem.

Emery Stora
77 Kingsley
Santa Fe, NM

 

[emerystora]

> Now, the generator , by a PO, is a 6.5kw Onan Emerald
>Plus, not the original Onan 6kw.
>Andy M PA
>75 PB

Andy - did you mention in an eariler posting that you did not have
the original Onan? Somehow I missed that fact. Your wiring as you
now describe it is definitely not stock GMC. The PO must have done
some rewiring when he installed the 6.5K Onan. Hopefully you are now
on the right track. Hope you find it soon. I know it must be
frustrating to you but look at what you have learned!

Let us all know your results.

Emery Stora
77 Kingsley
Santa Fe, NM

 

[emerystora]

>Emery,
> Hooray !!! The easy solution was the right one. I reconnected
>the wires, put both circuit breaker switches in the same position, started
>the generator, and had power everywhere. I even rotated the receptacle so the
>plug goes in easier as you suggested. The lesson - if you have an Emerald
>Plus Onan, you have two circuits off the generator and can lose half your
>power without losing all the power.
> Thanks for the help of those who responded. Now, on to other
>GMC challenges.
>
>Andy m, PA
>75 PB

Andy - Great !!! We were all pulling for you. Glad to hear that you
got it worked out.

Emery