Practical troubleshooting your RV, 101 #1

[Ralph L. Fullenwider]

Hello everyone;

Electrical systems in any venue, to many, is confusing and it does not have
to be. With just a few simple rules, one can do a systems check no matter
if it is a 12vdc/24vdc or an 110vac system.

The words, what? where?, how? and why? come to mind as the very basic start
to finding a problem with systematic troubleshooting.

What? equates to, What is the real problem? (does not mean what the problem
appears to be.)
Where? equates to the physical location of items along a "path" in a given
system.
How? equates to how does it or is supposed to work?
Why? (remember when Dad used to say "there is no such word as why." The why
equates to why did it happen in the first place.

It is important to try to learn how a system is designed to work or the
right way to say this is "know the sequence of operation." If you know how
it is supposed to work then you are ready to start trying to; "recognize"
"localize" and "isolate" a problem.

Ok lets pick a simple system; 12vdc fan. Problem, fan does not run. Ok so
now we know it is a fan not coming on, so the problem is "recognized." So
what do we really know about "where it is." A switch on a dash, the fan is
located behind a panel near the co pilots feet, but is there more in that
system besides a switch and fan motor? Could there be a "relay" in line
between the switch and fan? Could there be a circuit breaker or fuse,
between the switch and fan motor? All are valid questions and can be
answered with a "sequence" of operation.

"Sequence" of operation for the system above; 1.it is a 12vdc system so
from the system circuit breaker, 12vdc is supplied to a switch and from the
switch to the coil of a 12vdc relay then 12vdc passes through the contacts
of the relay to the fan motor and the fan motor runs.

Now we know the "how" it works, we can start to "localize" the problem.
Starting at the circuit break we are going to check for 12vdc to be sure
the switch is in fact getting power. Yes voltage is present. Then go to the
switch and check for 12vdc, yes voltage is present on one side, then switch
the switch to the run position and check for voltage. It is found that
12vdc is present on the out put side of the switch. Next stop is the relay
coil, check for 12vdc at the coil of the relay, yes 12vdc is resent, then
check the out put side of the relay, no voltage found, hmmm, interesting,
now it is time to find out how the relay works, 12vdc goes to the coil of
the relay then passes through the coil to ground and the relay energizes
and the contacts are changed in state for open to closed, but the 12vdc
power source is from some where else going to the 12vdc fan motor and not
the switch on the dash. Now one must check the voltage patch the flow
through the relay to the 12vdc fan motor, and find the "why" it is not
present. So we have isolated the part of the 12vdc circuit that is not
working to turn on the fan with the switch. Checking the "source" circuit
breaker, it is found not to have 12vdc present. So the circuit breaker is
the bad part, it must be replaced. Now switch on the dash switch and the
fan motor runs. Great! you have fixed the problem, or have you? Did we look
into the "why" the circuit breaker went bad? This part of trouble shooting
is not always well defined and in fact may not be found. So that brings up
the question, what must happen to make a circuit breaker fail? Lose
connections are a cause. Bad ground is a cause, age of the part will
contribute to the cause of failure.

As you can see there can be several steps and items in a system even one as
simple as this one. Trouble shooting can be VERY time consuming, but it has
to be done to make a system work. Once you have been through a few
troubleshooting procedures like this, you learn some short cuts here and
there that helps to "cut" the time factor down a bit.

Also a thing to remember. Nothing is set in concrete when trying to find
out and repair what does not work. What I am trying to do here is show a
process that is practical, saves time and effort and cuts the cost of a repair.

Let's not throw money at something in hopes that is will make it run. You
can sure go through allot of money doing that and still not find the
problem let alone fix it. So with a few trouble shooting steps we have
spent $3.00 on a part to make the system run, instead of spending $225.00
in parts like new switch? new fan motor, new relay and so forth. Yes it has
cost the time to troubleshoot the system but is still cheaper on a repair
bill than throwing money at some thing.

Will stop here for this first post and wait a few days and answer any
questions anyone may have.

Ues I know it is a VERY simple system noted above, but there are a large
percentage of people that do not have any idea what or how. Please keep
that in mind when posting on this first post.

Safe travels,

Ralph and Charolette Fullenwider
84FC35 "Ruff Diamond"
Duncan, Oklahoma