506860-03
Issue 1946
Page 15 of 27
Operation
The outdoor unit and the indoor blower cycle on demand
from the room thermostat. When the thermostat blower
switch is moved to the ON position, the indoor blower
operates continuously.
Filter Drier
The unit is equipped with a large capacity bi-flow filter
that keeps the system clean and dry. If replacement is
necessary, replace with one of similar design and capacity.
The replacement filter drier must be suitable for use with
R-410A refrigerant.
Crankcase Heater
If unit is equipped with a crankcase heater, it should
be energized 24 hours before unit start-up to prevent
compressor damage as a result of slugging.
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
stage by outdoor thermostats. When the room thermostat
is placed in the emergency heat position, the outdoor unit
control circuit is isolated from power and the field-supplied
relays bypass the outdoor thermostats. An amber indicating
light simultaneously comes on to remind the homeowner
that the unit is operating in the emergency heat mode.
Emergency heat is usually used during an outdoor
shutdown, but it should also be used following a power
outage if power has been off for over an hour and the
outdoor temperature is below 50°F. System should be left
in the emergency heat mode at least 6 hours to allow the
crankcase heater sufficient time to prevent compressor
slugging.
Pressure Switch Circuit
The control board includes two pressure switch circuits.
A high pressure switch is connected to the board’s HI-
PS terminals (see Figure 8). The low pressure, or loss-
of-charge pressure, switch is connected to the LO-PS
terminals.
During a single demand cycle, the control board will lock out
the unit after the fifth time that the circuit is interrupted by a
pressure switch wired to the control board. In addition, the
diagnostic LEDs will indicate a locked-out pressure switch
after the fifth occurrence of an open pressure switch.
The unit will remain locked out until power to the board
is interrupted, then re-established, or until the error is
cleaned.
NOTE
:
The control board ignores input from the low
pressure switch terminals as follows:
• During the TEST mode
• During the defrost cycle
• During the 90 seconds start-up period
•
For the first 90 seconds each time the reversing valve
switches heat/cool modes
Heat Pump Control-Defrost Operation
The defrost termination pins must be set on the heat pump
control prior to starting the system to ensure proper defrost
operation.
The heat pump control measures differential temperatures
to detect when the system is performing poorly because
of frost buildup on the outdoor coil. The heat pump control
self-calibrates when the defrost system starts and after
each system defrost cycle. The heat pump control monitors
ambient temperature, outdoor coil temperature, and total
run time to determine when a defrost cycle is required. The
coil temperature sensor is designed with a spring clip to
allow mounting to the outside coil tubing. The location of
the coil sensor is important for proper defrost operation.
NOTE
:
The heat pump control accurately measures the
performance of the system as frost accumulates on the
outdoor coil. This typically will translate into longer running
time between defrost cycles as more frost accumulates
on the outdoor coil before the heat pump control initiates
defrost cycles.
Defrost Operating Modes
The heat pump control operational modes are:
• Defrost calibration and operation
• Defrost test
Defrost Termination Temperature (J1)
The heat pump control can be set to terminate the defrost
cycle at 50, 70, 90, or 100°F (10, 21, 32 and 38°C) (see
Figure 8). The termination jumper is factory set at 50°F
(10°C). If the termination jumper is not installed, the default
termination temperature is 90°F (32°C).
NOTE
:
Colder climates may require a higher defrost
termination temperature setting to maintain a clear coil.
Second Stage Lock-In (J2)
For second-stage heat pumps, if the outdoor ambient
temperature is below the selected compressor lock-in
temperature, the second-stage compressor solenoid will
be energized even without a Y2 thermostat input. If the
jumper is not connected to one of the temperature selection
pins (40, 45, 50, 55°F) (see Figure 8), the second-stage
lock-in feature will not be activated. Factory default is 40ºF.
