506318-03
Page 14 of 18
Issue 1946
Operation
The outdoor unit and indoor blower cycle on demand
from the room thermostat. When the thermostat blower
switch is in the ON position, the indoor blower operates
continuously.
Emergency Heat Function (Room Thermostat)
An emergency heat function is designed into some room
thermostats. This feature is applicable when isolation of
outdoor unit is required or when auxiliary electric heat is
staged by outdoor thermostats.
For heat pumps equipped with outdoor thermostats, to
bypass electric heat, a field relay is required to properly
activate the emergency heat function of the room
thermostat.
Pressure Switch Connections
The unit’s automatic reset pressure switches (LO PS - S87
and HI PS - S4) are factory-wired into the control board on
the LO-PS and HI-PS terminals, respectively.
Low Pressure Switch (LO-PS
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. The low pressure switch is
ignored under the following conditions:
• during the defrost cycle and 90 seconds after the
termination of defrost
• when the average ambient sensor temperature is
below 15° F (-9°C)
• for 90 seconds following the start up of the compressor
• during “test” mode
High Pressure Switch (HI-PS)
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.
Pressure Switch Settings
• High Pressure (auto reset) - trip at 590 psig; reset at
418.
• Low Pressure (auto reset) - trip at 25 psig; reset at 40.
5-Strike Lockout Feature
The 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 will reset 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 current Y1 (Input),
the control will enter 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 between 1 and 2 seconds. All timer
functions (run times) will also be reset.
If a pressure switch opens while Y1 is engaged, a 5-minute
short cycle will occur after the switch closes.
Figure 7. Outdoor Unit Control Board
24V TERMINAL
STRIP
CONNECTIONS
DIAGNOSTIC
LEDS
HIGH PRESSURE
SWITCH
(OPTIONAL)
TEST
PINS
FIELD SELECT
TIMING PINS
REVERSING
VALVE
DEFROST
THERMOSTAT
LOW PRESSURE
SWITCH
(FACTORY SHIIPED)
COMPRESSOR
DELAY PINS
SERVICE LIGHT
CONNECTIONS
