
Low Pressure Switch (LO-PS)
The unit's automatic reset low pressure switch ($87) is fac-
tory-wired into the defrost board on the LO-PS terminals,
When the low pressure switch trips, the defrost board will
cycle off the compressor, and the strike counter in the
board will count one strike, ($87) is ignored under the fol-
lowing conditions:
• during the defrost cycle and 90 seconds after the ter-
mination of defrost
• when the average ambient sensor temperature is be-
low 15° F (-9°C)
• for 90 seconds following the start up of the compressor
• during "test" mode
High Pressure Switch (HI-PS)
The unit's automatic reset high pressure switch ($4) is fac-
tory-wired into the defrost board on the Ht-PS terminals.
When the high pressure switch trips, the defrost board will
cycle off the compressor, and the strike counter in the
board will count one strike.
Calibration of the board occurs after a defrost cycle to
ensure that there is no ice on the coil. During calibra-
tion, the temperature of both the coil and the ambient
sensor are measured to establish the temperature dif-
ferential which is required to allow a defrost cycle.
Before the start of each heating and cooling season, the
following service checks should be performed by a quali-
fied service technician,
•TURN OFF electrical power to the unit prior to unit
maintenance.
_WARNING
5-Strike Lockout Feature
• Internal control logic of the board counts the pressure
switch trips only while the Y1 (Input) line is active. If a
pressure switch opens and closes four times during a
Y1 (Input), the control logic resets the pressure switch
trip counter to zero at the end of the Y1 (Input). If the
pressure switch opens for a fifth time during the cur-
rent Y1 (Input), the control enters a lockout condition.
• The 5-strike pressure switch lockout condition can be
reset by cycling OFF the 24-volt power to the control
board or by shorting the TEST pins. All timer functions
(run times) will also be reset.
• If a pressure switch opens while the Y1 Out line is en-
gaged, a 5-minute short cycle will occur after the
switch closes.
Delay Mode
The defrost board has a field-selectable function to reduce
occasional sounds that may occur while the unit is cycling
in and out of the defrost mode. When a jumper is installed
on the DELAY pins, the compressor will be cycled off for 30
seconds going in and out of the defrost mode. Units are
shipped with jumper installed on DELAY pins.
NQTE -The 30 second off cycle is not functional when
jumpering the TEST pins.
Operational Description
The defrost control board has three operational modes:
1. Normal Mode - The demand defrost board monitors
the O line, to determine the system operating mode
(heat/cool), outdoor ambient temperature, coil tem-
perature (outdoor coil) and compressor run time to de-
termine when a defrost cycle is required.
2. Defrost Mode - See table 10 for defrost mode and de-
mand defrost operation.
3. Calibration Mode - The board is considered uncali-
brated when power is applied to the board, after cool
mode operation, or if the coil temperature exceeds the
termination temperature when it is in heat mode.
• Inspect and clean the outdoor and indoor coils. The
outdoor coil may be flushed with a water hose.
NQ TE -It may be necessary to flush the outdoor coil
more frequently if it is exposed to substances which
are corrosive or which block airflow across the coil
(e.g., pet urine, cottonwood seeds, etc.).
• Visually inspect refrigerant lines and coils for leaks.
• Check wiring for loose connections.
• Check voltage at indoor and outdoor units during op-
eration.
• Check the amp-draw at the outdoor fan motor, com-
pressor, and indoor blower motor. Compare readings
with values given on unit nameplate.
• Clean or replace indoor unit filters.
• Check refrigerant charge and system pressures.
• Check condensate drain line for free and unobstructed
flow; clean if necessary.
Outdoor unit fan motor is prelubricated and sealed. No
further lubrication is needed.
NQ TE -If owner reports insufficient cooling, the unit
should be gauged and refrigerant charge checked.
(See Refrigerant Charging on Page 13.)
Refer to the Engineering Handbook for optional accesso-
ries that may apply to this unit, e.g.:
• Loss of Charge Kit
• Compressor Monitor
• Hail Guards
• Mounting Bases
• Timed Off Control
• Stand-off Kit
• Sound Cover
• Low Ambient Kit
• Monitor Kit
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504867M 06/06