Service Manual

53
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 for 4 minutes during the interval.
The defrost cycle is terminated when the coil temperature
reaches 65_F or 10 minutes has passed.
On *CH6 models, defrost will occur in low- or high- stage as
demanded by the thermostat or wall control regardless of
OAT.
On *CH9 models, when OAT is >25_F(-3.9_C), defrost will
occur in low- or high- stage as demanded by the thermostat
or wall control.
On *CH9 models, if OAT is ≤25_F(-3.9_C), defrost will
occur in high- stage only, regardless of thermostat or wall
control demand, and will terminate at 50_F(10_C) coil
temperature with a minimum of 2.5 minutes in defrost.
If the coil temperature does not reach 32_F(0_C) within the
interval, the interval timer will be reset and start over.
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)
outdoor ambient temperature.
The outdoor fan output (ODF) will remain off for 20 seconds
after termination. This delay will allow time for the system to
capture the heat from the outdoor coil and reduce the
“steam cloud” effect that may occur on transition from
defrost to the heating cycle. The outdoor fan output OFF
delay of 20 seconds may be defeated to enable the fan to
energize immediately at the time of termination and 12
seconds prior to the reversing valve de- energizing, through
forced defrost pins as follows:
S The ODF fan delay defeat can be toggled by
shorting the forced defrost pins for >15 seconds
while in the standby mode (status LED on solid).
The LED will start to flash when the toggle has
taken place.
S Status code 4 shows the fan delay defeat is active
(no delay)
S Status code 3 shows that it is not active (20
second delay)
The code will continue to be displayed until after the short is
removed. Once the short is removed, there is a 5 second
wait before the code is cancelled. The code that is flashing
will finish before going back to solid LED. The control is
shipped with the ODF fan delay defeat NOT active. The
change in status is remembered until toggled to a new
status. A power down / power up sequence will not reset the
status. It may be necessary to do the toggle twice to cycle to
the desired state of defeat.
Defrost
Hold
In a non- communicating system, if the thermostat becomes
satisfied (Y1 or Y1 and Y2) before the defrost cycle is
terminated, the control will “hold” in defrost mode and finish
the defrost cycle on the next call for heat.
With Communicating control, defrost hold is not needed in a
Communicating system because the wall control will
complete the defrost cycle before shutting down the system.
Forced
Defrost
With non- communicating control, forced defrost can be
initiated by manually shorting the 2- pin header labeled
FORCED DEFROST (see Fig 42) on the control board for 5
seconds then releasing.
With Communicating control, forced defrost is initiated with
the wall control.
On all models, during a Forced Defrost:
S If coil temperature is at defrost temperature of
32_F, and outdoor air temperature is below 50_F, a
full defrost sequence will occur.
S If coil temperature or outdoor air temperature does
not meet the above requirements, an abbreviated
30 second defrost will occur.
S Both Quiet Shift and Quiet Shift- 2 compressor ON/
OFF delays will be included in a forced defrost if
either are enabled.
Quiet Shift- 2 (Communicating models)
(FAST # 1185237, 1186140)
Quiet Shift- 2 is a field selectable defrost mode which may
eliminate occasional noise that could be heard at the start
and finish of the defrost cycle.
On a non- communicating system, this feature must be
enabled by selecting the 3rd position of the 3- position dip
switch on the outdoor control board. For Communicating
systems, it must be enabled at the wall control. When
activated, the following sequence of operation occurs:
Defrost Initiation – The compressor is de- energized for 70
seconds. During this 70 second compressor off time, the
reversing valve will be energized. Once the 70 second
compressor off time has been reached, the compressor will
be energized then the outdoor fan will be de- energized at
which time the normal defrost cycle begins.
Defrost Termination – the outdoor fan will be energized
shortly before the compressor is de- energized for 60
seconds. During the compressor 60 second off time, the
reversing valve will be de- energized. Once the 60 second
compressor off time has been completed, the compressor
will be energized at which time the system will be in normal
heat 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 Split System Long Line Applications Guidelines
for long- line application details.
Accessory Liquid Solenoid with
Communicating
Control:
When using the Communicating control, the liquid- line
solenoid output is provided at the Y1 connection. 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.
On Models with Accessory Liquid Solenoid Using
a
Non- Communicating
Thermostat:
The liquid solenoid is connect to the Y1 and C terminal
connections. The liquid solenoid closes, in the compressor
off mode, to prevent refrigerant migration into the unit
through the liquid- line.