Fan Switches; Limit Switches - Coleman 7600 Service Manual

INSTALLATION
INSTRUCTIONS
FAN SWITCHES
'I'he furnace
is
equipped
with
one
fan
switch
located
at the top
of the control panel. This switch
is
a
nor-
mally open switch that
closes
with a
rise
in
tempera-
ture. The fan switch
is a
disc type switch
that
is
calibrated
to
close
at 105',
and
open
at
90o.
As
in
the
case
ol a limit switch, the
temperature
on
the
fan
switch
does
not
necessarily
mean
that the
air
will
be
the
same temperature.
A fan switch, due
to
its
loca-
tion on the
furnace,
might actually start
the
blower
at
an outlet air
temperature
that is
above
the
calibrated
temperature.
The disc
switches used
are marked
to
indicate the
tem-
perature
at
which the switch
will
open
or
close
and the type switch being used.
For example,
a
marking
of
Fl40-30 means
that the switch is a fan
switch
set
to
turn the
blower
on
at
l40o and shut
of
at
ll0o
(140-30=
I
l0).
ELECTRICAL
TERMINALS
THRUST
EUTTON
BI.METAL OISC.:
HOT
CIRCUIT CLOSED
FAN
SWITCH
LIMIT
SWITCHES
Each furnace
is
equipped
with two limit
switches. The
upper
limit
switch
is
located
on the left
side
of
the
blower housing
in the blower compartment. The
upper
limit
shuts
the furnace
off in
case
the upper portion of
the furnace overheats.
An
overheating
condition
could
exist
at the top
of
the furnace
because
of
circulating
blower failure. electrical failure,
or
overfiring
of
the
furnace.
The lower limit
shuts
the
lurnace
olf in
case
of
exces-
sive
heat build
up in the lower portion
ol
the
furnace'
The lower
limit switch is
located
at
the bottom
of
the
control wiring box.
Some
common causes
of
overheating
in
this
region
are
restricted ducts,
too
many floor
registers closed,
or
restricted
inlet, i.e.
dirty
filter,
clothes
hanging near
or over the
inlet
area.
The lower
limit will
automatically reset
when the
air
temperature has cooled down.
The disk thermoswitch
is
operated
by the heating
and
cooling
of a
bi-metal
disk. Under
"hot"
conditions,
the bi-metal disk
will
snap inward thrusting
the
elec-
trical contacts open; thereby breaking
the
electrical
circuit. Upon cooling, the bi-metal disk
will
snap
back
out and let the contacts close
which
will
then let
elec-
trical power
pass
through without interruption.
ELECTRICAL
MOVEAELE
CONTACT
BI.METAL
DISC.. HOT
CIRCUIT OPEN
Br-METAL
OrSC.
-
COOL
crRcutT cLosEo
LIMIT
SWITCH
MOVEABLE
CONTACT
MOVEABLE
CONTACT
BI.METAL
DISC.--
COOL
CIRCUIT OPEN
l5