9
Standard Thermostat low ambient cooling mode:
A Low Ambient Pressure Switch kit, Evaporator Freeze
Thermostat and Isolation Relay must be installed for low ambient
operation in standard thermostat mode. The fan motor is a
ball--bearing type and does not need to be changed. A crankcase
heater must be installed. See Product Data for part numbers on
appropriate unit size and series units.
DEFROST
This control offers 4 possible defrost interval times: 30, 60, 90 or
120 minutes. These are selected by dip switches on the unit
control board, or in the Evolution control (if used). The
Evolution Control selection overrides the control board dip
switch settings.
Auto defrost is available with Evolution communicating control
only and it must be enabled in the User Interface. Auto defrost
adjusts the defrost interval time based on the last defrost time as
follows:
S
When defrost time is < 3 minutes, the next defrost
interval = 120 minutes
S
When defrost time is 3--5 minutes, the next defrost
interval = 90 minutes
S
When defrost time is 5--7 minutes, the next defrost
interval = 60 minutes
S
When defrost time is > 7 minutes, the next defrost
interval = 30 minutes
The control board accumulates compressor run time. As the
accumulated run time approaches the selected defrost interval
time, the control board monitors the coil temperature sensor for a
defrost demand. If a defrost demand exists, a defrost cycle will be
initiated at the end of the selected time interval. A defrost demand
exists when the coil temperature is at or below 32
_
F/0
_
C for 4
minutes during the interval.
The defrost cycle is terminated when the coil temperature reaches
65
_
F/18.33
_
C or 10 minutes has passed.
If the coil temperature does not reach 32
_
F/0
_
C within the
interval, the interval timer will be reset and start over.
NOTE
:
S
Upon initial power up the first defrost interval is defaulted
to 30 minutes. Remaining intervals are at selected times.
S
Defrost is only allowed to occur below 50
_
F/10
_
C out-
door ambient temperature.
Defrost Hold
In a non--communicating system, if the thermostat becomes
satisfied before the defrost cycle is terminated, the control will
”hold” in defrost mode and finish the defrost cycle on the next
call for heat. Defrost hold is not needed in a communicating
system because the User Interface will complete the defrost cycle
before shutting down the system.
Forced Defrost
Forced defrost can be initiated manually in a non--communicating
system, or by communicated command from a User Interface.
The board contains a 2--pin header labeled FORCED DEFROST
(See Figure 14). To initiate a forced defrost:
S
Manually, short FORCED DEFROST pins for 5
seconds then release
S
If coil temp is at defrost temp of 32
_
F/0
_
C, and out-
door air temperature is below 50
_
F/10
_
C, a full defrost
sequence will occur
S
If the coil temp or outdoor air temperature do not meet
the above requirements, an abbreviated 30 second de-
frost will occur
QUIET SHIFT
This feature must be enabled by selecting the 3rd position of the
3--position dip switch for a non--communicating system or
enabling it at the User Interface in an Evolution communicating
system. Quiet Shift is a field selectable defrost mode that, when
activated, will eliminate occasional compressor sound that could
be heard at the start of defrost cycle and restart of heating cycle.
When the Quiet Shift is activated, and a defrost is initiated, the
following sequence of operation will occur. Reversing valve will
energize, compressor will turn off for 30 seconds, and then turn
back on to complete defrost.
At the start of heating after
conclusion of defrost, reversing valve will de--energize,
compressor will turn off for another 30 seconds, and the fan will
turn off for 40 seconds, before starting in the heating mode.
LIQUID LINE SOLENOID ACCESSORY
In heat pump long line applications, a liquid line solenoid is
required to control refrigerant migration in the heating mode. The
solenoid should be installed near the outdoor unit with the arrow
facing the outdoor unit. This is the direction of flow control. See
Long Line Application Guideline for details.
Accessory Liquid Solenoid with Evolution Communicating
Control: When using the Evolution Control, a liquid line solenoid
output labeled LS is provided. Connect the solenoid as shown in
the wiring label diagram. This is a 24vac output that is energized
whenever the compressor is energized. It closes in the
compressor--off mode to prevent refrigerant migration into the
unit through the liquid line.
Accessory
Liquid
Solenoid
with
Non--Communicating
Thermostat: The liquid solenoid is connected to the Y and C
terminal connections.
The liquid solenoid closes in the
compressor--off mode to prevent refrigerant migration into the
unit through the liquid line.
MAJOR COMPONENTS
Control Board
The Heat Pump control board controls the following functions:
S
Compressor contactor operation
S
Outdoor fan motor operation
S
Reversing valve operation
S
Defrost operation
S
Compressor external protection
S
Pressure switch monitoring
S
Time delays
Field Connections
The control receives 24vac low--voltage control system inputs
through the R, C, Y and O thermostat connections located at the
bottom of the control board (see Fig. 11) or the ABCD Evolution
connector at the bottom of the control board. The 24vac control
output terminal connection W2 is used during defrost. On
Evolution only, the 24vac LS (liquid solenoid) output terminal is
energized for the liquid solenoid accessory. The connection is
located at the bottom of the control board.
Compressor Internal Relief
The compressor is protected by an internal pressure relief (IPR)
which relieves discharge gas into the compressor shell when
differential between suction and discharge pressure exceeds
550--625 psi. The compressor is also protected by an internal
overload attached to motor windings.
264A
/265A
