Hired-Hand Farm Hand Series: SCS w/Back-Up - Manual (Page 9)

Part No. 4801-5117 Rev. 8-01 Farm Hand SCS 7
it warms the building at least 2
°
. The same is true if the temperature goes above the High Limit
however, there are three levels of cooling stages on the Back-Up System. The following example
explains the operation of the stages in relationship to the temperature and the limits.
In this example the Low Limit is set as 66ºF, and the High Limit is set as 86ºF. If the temperature
drops to 66ºF, then the HEAT stage turns on. The HEAT stage turns off when the temperature rises to
68ºF (2º above the Low Limit). If the temperature rises to 86ºF, then COOL 1 turns on. If the
temperature continues to rise to 88ºF (2º above the High Limit), then COOL 2 turns on. If the
temperature rises to 90ºF, then COOL 3 turns on. Stages turn off at temperatures as indicated by the
arrows in graph 1.
8.2 Emergency Operation
In this mode of operation, the system still maintains the temperature as it does in Normal Operation.
In addition, it will begin running the first cooling stage (Cool 1) on a 5 minute timer. The timer
percentage is determined by the setting in P3 (Emergency Timer Percentage). This mode of operation
is entered if communication is lost between the master controller and the Back-Up System. In this
case, the Back-Up System assumes that the master controller is lost and tries to maintain the minimum
ventilation until someone recognizes the problem. Emergency Operation is indicated by a “LnE”
flashing in the display of the Back-Up System. The alarm relay on the Back-Up System is also
engaged in this mode operation.
8.3 Override Operation
In this mode of operation, the system still maintains the temperature as it does in Normal Operation.
In addition, it receives commands from the master controller to turn on certain stages of heating or
cooling. There are many different circumstances that could cause this to happen, in this manual, we
will list one of the most common. For example, if communication were lost from the SCS™ panel to
the master controller, the master controller would be unable to turn the appropriate stages on in the
usual way. Therefore, the master controller would communicate to the Back-Up System and indicate
which stages that it is trying to turn on. At this point, the Back-Up System would obey the command
and turn the appropriate stages on. For this mode of operation to work to its fullest potential, care
must be taken to insure that the stage jumpers on the relay strips match the stage setting in the master
controller (Refer to Section 12). Override Operation is indicated by a “LnO” flashing in the display of
the Back-Up System. The alarm relay is also engaged in this mode of operation.
8.4 Fail-Safe Relay Operation
There are two types of Relay strips used in the SCS™. The Normally Open (NO) strip requires a
signal from the controller board in order to energize a stage of ventilation. Should power be removed
from the SCS the Normally Open Relay strips would not be able to energize a ventilator. On the other
6 4 6 8 7 2 7 6 8 0 8 4 8 8 9 2
H e a t
C o o l 3
C o o l 2
C o o l 1
Temperature (ºF)
Graph 1 Cool 1, 2, 3 and Heat