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The defrost control is a solid state control
manufacturedby Hamilton Standard.The control
providesautomaticswitchingfrom normal heating
operationto defrost mode and back.The defrost
controlcontains a solidstatetimerwhich switches an
externa] defrost relay through 1/4" male spades
mountedon the control'scircuit board.Thecontrol
energizes t he defrostrelay
at regular timed intervals.
On some units, a normally
open defrost switch placed
in series between
the defrost
relay and the control
initiates
defrost only when needed at the end of the
timed
intervals.
On other units, the control
initiates
defrost
on demand from the defrost thermostat,
7- Timing Jumper
A factory
installed jumper
on the circuit
board
connects terminal
Wl on the circuit board to one
of the three timing
pins.
8- TST Pins
Each board is equipped
with a test pins for use in
troubleshooting
the
unit.
When
jumpered
together,
these pins reduce the control timing
to
about 1/256 original
time.
A CAUTION
Defrost Control Components:
1- 24V Terminal
Terminat
24V receives 24VAC from
the control
transformer.
This terminal
powers
the control's
internal
timer and relays. Terminal
24V must be
powered
at all times to provide
HOLD between
thermostat
demands.
2
COM Terminal
Terminal
COM provides 24VAC common.
3- HLD Terminal
Terminal
HLD hold the internal
timer
in place
between thermostat
demands and altows the unit
to
continue
timing
upon
resumption
of
thermostat
demand,
tn most units, terminal
HLD
is connected
directly
to thermostat
demand.
4- OUT Terminal
Terminal
OUT
controls
unit
defrost
when
connected
to one side of the defrost
relay coil. An
internal
relay connected
to terminal
OUT closes
to allow
external
defrost
relay to energize
and
initiate defrost. At the end of the defrost
period,
the
internal
relay
connected
to terminal
OUT
opens to de-energize
the external
defrost relay.
5- RST Terminal
This terminal
is not functional
for the specified
application.
6- Timing
Pins (T1,T2,T3)
Each of these
pins provides
a different
timed
interval
between
defrosts (30, 60 or 90 seconds).
A jumper
connects
the
pins
to circuit
board
terminal
Wl.
To change
the interval
between
defrosts,
remove
the jumper
from
the pin it is
connected
to and reconnect
the jumper
to one of
the other available
pins.
To Place Control in Test Mode:
1- Turn off all power to avoid damaging
the circuit
board.
2- Make sure all control terminats
are connected
as
shown on unit wiring
diagram before attempting
to place control
in test mode.
IMPORTANT
3- Connect jumper to "TST" pins,
4- Turn indoor thermostat
to heat mode and adjust
to highest temperature
setting.
5- See table 1 for control timings in "TST"
mode,
6- Turn on power to unit and re-adjust thermostat.
Be sure to remove jumper when test is complete.
TABLE 1
TEST MODE CONTROL TIMINGS
NORMAL
!_ 30+3
60±6
:
90_9
_
14+1,4
OPERATION
MIN
MIN
i
MIN.
MIN.
"TST"
PINS
1!7+0r7
14+1A
i 21_+21
3-3_0.3
JUMPERED
SEC.
i
SEC
i
SEC*
i
SEC
TOGETHER
!
Page 3
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