Unit installation

40 Microprocessor Control
3.10.2 C/F Degrees
The control may be selected to show readings and setpoints in either degrees Fahrenheit (°F) or in
degrees Celsius (°C). To change the value use
ENTER
to select this function, then use the
UP/
DOWN
arrow to change the value. Press
ENTER
to store the value.
3.10.3 Humidity Control Method
The operator may select either relative (direct) or absolute (predictive) humidity control. If “rela-
tive” is selected, the RH control is taken directly from the RH sensor. If “absolute” is selected, the
RH control is automatically adjusted whenever return air temperature deviates from the desired
temperature setpoint (i.e., predictive humidity control). The LCD display will indicate percentage
relative humidity for both methods of control. If the “absolute” feature is selected, the adjusted
humidity reading will also be shown. When utilizing the predictive humidity control feature, the
humidity level is automatically adjusted ~2% RH for each degree difference between the return
air temperature and the temperature setpoint.
Unnecessary dehumidification can result when overcooling occurs during a dehumidification
cycle. This is due to a higher than normal RH reading caused by overcooling the room (about 2%
RH for each degree of overcooling). This drop in temperature extends the dehumidification cycle.
Later, when the dehumidification ends and the temperature rises to the setpoint, the RH reading
falls. The final RH reading will then be lower than actually desired. If the temperature drop was
significant enough, the percentage RH could be low enough to activate the humidifier.
If the absolute humidity control is selected, over-dehumidification may be avoided. When over-
cooling occurs (i.e., causing an increase in the RH reading) the humidity control program esti-
mates what the RH will be when the dehumidification cycle ends and temperature returns to the
setpoint. This allows the dehumidification cycle to end at the proper time. Predictive humidity
control can greatly reduce energy consumption by minimizing both compressor/reheat operation.
Use the
UP/DOWN ARROW
key to select the desired humidity control method.
3.10.4 Lead Compressor
This function allows the user to select which compressor is the lead: Compressor 1 (3 ton), Com-
pressor 2 (5 ton), or Auto. The factory default is Auto. If Auto is selected, the control will deter-
mine which compressor is to be the lead compressor based on the average room load over the
previous one hour of operation.
3.10.5 Show DIP Switch
This function shows the position of the DIP switches which are located on the control board in the
unit. 1 = Switch is “ON” and 0 = Switch is “OFF”. For more information on the DIP switches and
their functions, see Table 17 Equipment Switch Settings.
3.10.6 Valve Time (for systems with a modulating chilled-water valve)
This function shows the full valve travel time of the modulating valve on a chilled-water system.
This is the time it takes for the valve to travel from full closed to full open. It is programmable
from 50 to 250 seconds; factory default time is 165 seconds and should not be changed unless
actual valve travel time is not correct. The full valve travel time is used by the control to deter-
mine the appropriate valve position. For example, if the valve travel time is 165 seconds and 50%
cooling is being called for, the valve will open for 83 seconds to achieve 50% open.
3.10.7 CW Flush (for systems with a modulating chilled-water valve)
This function shows the interval time at which the system will perform a modulating chilled-
water valve system flush cycle. The factory default is 24 (hours) and is programmable from 0
(hours) which signifies to never flush, to 99 (hours) which signifies to flush after every 99 hours of
valve non-use. If the valve is called on by the control to open within the programmed interval
time, the timer will be reset to 0. The flush cycle is active even when the fan is turned off, but
power is applied to the unit. When the interval timer reaches the programmed time, the valve will
be opened for 3 minutes to flush any contaminates which may have collected in the system.