www.fueloilnews.com | FUEL OIL NEWS | AUGUST 2014 45
thermostats anyway. With a jumper the customer can end up
with an 'overheating' call-back, but with a turned up thermostat
they can fix the problem themselves. I realize another issue comes
up with the electronic thermostats that provide 'adaptive intel-
ligent' functions. By turning these thermostats up and turning off
the burner while servicing them, you may 'fool' the thermostat
into another mode of operation and cause another call-back. It
is always best to disconnect one of the T-T leads before doing
anything.
The problems we are looking at are mostly from putting
jumpers across the wrong terminals of the fan center and causing
damage. I'm also hearing about relays that stay pulled in due to
all of the quirks associated with low voltage wiring. I guess with
all the problems aside we are going to have to learn to live with
the fan center and low voltage limits, so let's take a closer look at
the relay in question and its wiring in Figure 7. You can see that
there are two voltages in use here and that I have not put in the
air conditioning components that are normally shown in most
drawings of this type (Figure 8). By the way, and it's only my
opinion, although many boilers now also use fan centers for vari-
ous reasons I do not agree with the practice due to the mistakes
we are looking at and the amperages involved. A fan center is just
that, period.
Figure 4, Figure 5 and Figure 7 are from my series WIRING
and Fuel Burning Equipment, and since we focus on heating we
do not add AC wiring except in the cases where we note it. As you
can easily see we are showing only the wiring diagram and have
deleted the contacts and relay functions in Figure 7 as well as the
AC function in Figure 8 leaving just the thermostat and fan con-
nections for heating and cooling.
The fan center is a 'mixed voltages' device and if you don't
check the contact you put a meter or jumper on damage can
occur. In addition, don't forget many new transformers now
include a non-replaceable fuse that will blow and ruin the trans-
former with dead shorting. Just follow the wiring diagram, use a
meter to qualify and quantify your readings and be careful when
working around mixed voltage devices.
See ya.
George Lanthier is the owner of Firedragon Academy, a
Massachusetts Certified School teaching gas, oil and heating sys-
tem design and wiring and other related subjects. Firedragon is
also a publishing and consulting firm to fuel companies, utilities,
insurance companies and attorneys. George is the author of over
50 books and manuals on gas and oil heating and HVAC subjects.
He is a CETP, NATE, NORA, PMAA and PMEF Proctor and a
Massachusetts Certified Instructor. His website can be found at www.
FiredragonEnt.com
HVAC/ HydroniCs
Figure 7
Figure 8
Figure 6
l F o n
