Installation guide
DEFROST
SYSTEM
A.
DEFROST
THERMOSTAT
The
defrost
thermostat
is
factory
installed
on
a
short
tube
stub
extending
from
the
coil
end
plate.
Refer
to
Figure
12
and
confirm
that
the
thermostat
is
securely
fastened
in
place
on
the
tube
stub.
Figure
12
Defrost
Thermostat
FEEDER
TUBE
[
STUB
COIL
\
DEFROST
THERMOSTAT
B.
DEFROST
CONTROL
BOARD
The
defrost
board
is
a
time/temperature
control
which
includes
a
field-selectable
time
period
between
defrost
cycles
of
30, 60,
or
90
minutes
(quick-connects
located
at
board
edge,
factory
set
at
90
minutes).
Defrost
mode
is
identical
to
cooling
mode
except
that
outdoor-fan
motor
stops
and
second-stage
heat
is
turned
on
to
continue
warming
conditioned
space.
Initially,
the
defrost
cycle
timer
starts
when
the
contactor
is
energized
and
a
24
VAC
signal
is
present
on
the
T1
terminal.
Then
the
defrost
cycle
begins
when
the
defrost
thermostat
is
closed
and
the
cycle
timer
times
out
(30,
60,
90
or
minutes).
There
are
two
timers
involved
in
the
defrost
sequence:
Interval
Timer
—
30,
60,
or
90
minutes,
selected
by
setting
the
jumper
on
the
defrost
board.
Timer
is
only
active
during
calls
for
heating.
Timer
starts
when
the
defrost
thermostat
closes
32°F
(0°C).
Timer
stops
when
a
defrost
is
initiated
by
the
defrost
board
or
when
the
defrost
thermostat
opens
65°
F
(18°C).
Defrost
Timer
—
10
minutes,
not
adjustable.
Timer
is
only
active
while
the
coil
is
defrosting.
Timer
starts
when
the
defrost
board
initiates
a
defrost.
Timer
stops
when
the
defrost
thermostat
opens
65°
F
(18°C)
or
after
timing
out
at
10
minutes
(whichever
comes
first).
SPEEDUP
pins
are
provided
on
the
defrost
board
to
heip
in
troubleshooting
without
waiting
for
timers
to
expire.
Jumpering
the
SPEEDUP
pins
causes
any
active
timer
to
run
very
fast
(256
times
normal
speed).
Jumpering
the
SPEEDUP
pins
does
not
by
itself
initiate
any
timers,
it
only
affects
timers
that
are
already
running
or
are
already
part
of
the
sequence.
To
initiate
a
forced
defrost
cycle
(test
cycle),
the
defrost
thermostat
(Figure
12)
must
be
closed.
There
are
two
ways
to
verify
that
the
defrost
thermostat
is
closed:
4.
Jumper
across
the
DFT
terminals
on
the
defrost
board
(Figure
13).
With
this
method,
the
defrost
thermostat
is
removed
from
the
circuit,
and
operation
of
the
defrost
thermostat
itself
will
not
be
observed.
Skip
to
#3.
Use
a
volt-meter
to
confirm
there
is
no
voltage
across
the
DFT
leads.
24
volts
across
the
SFT
terminals
indicates
an
OPEN
defrost
thermostat.
Zero
volts
across
the
DFT
terminals
indicates
a
CLOSED
defrost
thermostat.
With
this
method,
the
operation
of
the
defrost
thermostat
can
be
observed
during
the
test.
If
the
defrost
thermostat
is
confirmed
closed,
skip
to
#83.
If
the
defrost
thermostat
is
open
(24
volts
across
DFT
leads)
it
may
be
possible
to
close
the
defrost
thermostat
by
forcing
a
frost
buildup
on
the
outdoor
coil.
Follow
these
steps:
¢
Turn
off
power
to
unit.
*
Disconnect
outdoor
fan-motor
lead
from
OF2
on
control
board
(Figure
13).
Tape
lead
to
prevent
grounding.
e
Restart
unit
in
heating
mode;
wait
for
accumulation
of
frost
on
outdoor
coil.
Use
volt-meter
to
confirm
there
are
zero
volts
across
the
DFT
leads
(thermostat
closed).
¢
Turn
off
power
to
unit.
Replace
outdoor
fan-motor
lead
to
OF2
on
control
board
(Figure
13).
Restart
the
unit
in
heating
mode.
With
unit
running
in
heating
mode
and
the
defrost
thermostat
closed,
the
entire
defrost
sequence
can
be
sped
up
for
testing
by
shorting
together
the
SPEEDUP
pins
on
the
defrost
board.
Use
a
flat-headed
screwdriver
to
short
the
pins
together.
Hold
the
SPEEDUP
pins
shorted
together
until
the
reversing
valve
shifts.
SPEEDUP
reduces
whatever
time
was
left
on the
interval
timer
(80/60/90
minutes).
In
normal
operation
the
reversing
valve
will
always
shift
with
the
SPEEDUP
pins
shorted
for
between
1
and
21
seconds.
After
shorting
the
SPEEDUP
pins
together
as
described
in
#4,
the
reversing
valve
will
energize
(shift
to
AC
mode),
the
outdoor
fan
will
stop,
the
strip
heat
will
energize,
and
the
coil
will
begin
to
defrost.
There
are
two
options
for
the
defrost
test:
a.
Remove
the
short
from
between
the
SPEEDUP
pins
immediately
after
the
reversing
valve
shifts,
and
the
unit
will
defrost
for
a
shortened
period
of
time
(something
less
than
10
minutes).
The
defrost
will
stop
when
the
defrost
thermostat
opens
(reaches
65°
F)(18°
C)
or
when
the
defrost
timer
times
out
(something
less
than
10
minutes).
b,
Leave
the
SPEEDUP
pins
shorted
together
for
more
than
2
seconds
after
the
reversing
valve
shifts,
and
the
unit
will
immediately
return
to
heating
operation
(#6
below).
Continue
to
leave
the
pins
shorted
together
and
the
sequence
starts
over
at
#4
above.
Unit
returns
to
heating
mode
after
defrost
sequence.
Reversing
valve
shifts
back,
outdoor
fan
starts
up,
and
strip
heat
de-energizes.
12
428
01
5103
02