Service Manual

45
Fig. 33 – Control Board 1190261 (for units with ECM Fan Motor)
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 outdoor
ambient temperature.
S The Quiet Shift- 2 compressor on/off delays, as described
below, will be included in a forced defrost if Quiet Shift- 2
is enabled.
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 Wall Control 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 Wall Control. The board contains a 2- pin header
labeled FORCED DEFROST (See Figure 13). 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 outdoor 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 defrost
will occur
QUIET SHIFT- 2
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. For installations using a
standard 2- stage thermostat, this feature must be enabled
by selecting the 3rd position dip switch on the outdoor
control board. For installations using an Observer Wall
Control, this feature 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
Term in a tio n - 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 d
e 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.