33
Start Up Delay Time (DLAY)
This option delays the unit from operating after a power reset.
The configuration may be adjusted from 0 to 900 seconds of
delay.
TSTAT — Both Heat and Cool (STAT)
When this configuration is set to yes the TSTAT alert for si-
multaneous Heat and Cool calls is disabled. This will not allow
heating and cooling to operate simultaneously.
Auxiliary Relay Configuration (AUX.R)
This option configures the auxiliary relay on the MBB
(RLY11). The function of this relay is configurable in the fol-
lowing ways:
• AUX.R = 0 (Alarm Output) — The relay is used for re-
mote annunciation of an alarm state.
• AUX.R = 1 (Dehum-Reheat) — The relay is used as a de-
humidification/reheat output.
• AUX.R = 2 (Occup. State) — The relay is used to reflect
occupancy. When the control is in occupied mode, the re-
lay will be ON. When the control is in unoccupied mode,
the relay will be OFF.
• AUX.R = 3 (S. Fan State) — The relay is used to reflect
the supply fan commanded state. When the supply fan is
on, the relay will be ON. When the supply fan is off, the
relay will be OFF.
Space Temp Sensor (SPT.S)
If a space temperature sensor is installed, this configuration
should be enabled.
Space Temp Offset Sensor (SP.O.S)
If a space temperature sensor with a space temperature offset
slider is installed (T56), this configuration should be enabled.
Space Temp Offset Range (SP.O.R)
If a space temperature offset sensor is installed, it is possible
to configure the range of the slider by adjusting this range
configuration.
Return RH Sensor (RRH.S)
If a return air relative humidity sensor is installed, this configu-
ration should be enabled.
Filter Status Switch Enabled? (FLT.S)
If a filter status switch is installed, enable this configuration to
begin the monitoring of the filter status input (Inputs
GEN.I
FLT.S). See the Dirty Filter Switch section on page 60 for
more details on installation and operation.
Cooling Control
When mechanical cooling is required, the A Series ComfortLink
control system has the capability to control the staging of the
compressors in several different ways. Three scroll compressors
are used on sizes 020 to 027 and four on sizes 030 to 060. In ad-
dition, the ComfortLink control system supports the use of an
optional minimum load hot gas bypass valve (MLV) that is di-
rectly controlled by the ComfortLink control system. This pro-
vides an additional stage of capacity as well as low load coil
freeze protection. The control also integrates the use of an econ-
omizer with the use of mechanical cooling to allow for the great-
est use of free cooling. When both mechanical cooling and the
economizer are being used, the control will use the economizer
to provide better temperature control and limit the cycling of the
compressors. The control also checks on various other operation
parameters in the unit to make sure that safeties are not exceeded
and the compressors are reliably operated.
The A Series ComfortLink control system offers two basic
control approaches to mechanical cooling. Constant volume
operation for 2 stages of cooling or VAV operation for multiple
stages of cooling. In addition to these methods of control, the A
Series ComfortLink control offers the ability to run multiple
stages of cooling for either a space temperature sensor or ther-
mostat by controlling the unit to either a low or high cool sup-
ply air set point. The control type (Configuration
UNIT
C.TYP) determines the selection of the type of cooling control
as well as the method for selecting a cooling mode.
There are either three or four compressors divided among two
refrigeration circuits in the unit. Circuit A always contains two
compressors (A1,A2). Circuit B has either one or two compres-
sors (B1,B2). There may be a minimum load valve (MLV),
which, if present, is only associated with circuit A. The deci-
sion as to which compressor should be turned on or off is de-
cided by the compressor’s availability followed by a preferred
staging order.
NOTE: Configuration of the machine control type (C.TYP) has
no effect on whether a unit has a VFD or just a supply fan in-
stalled for static pressure control. No matter what the control
type is, it is possible to run the unit in either CV or VAV mode
provided there are enough stages to accommodate lower air vol-
umes for VAV operation. Refer to the section on static pressure
control for information on how to set up the unit for the type of
supply fan control desired.
SETTING UP THE SYSTEM
Machine Control Type (Configuration
UNIT
C.TYP)
The most important cooling control configuration is located
under Configuration
UNIT.
This configuration defines the method and control source re-
sponsible for selecting a cooling mode. The configuration also
determines the method by which compressors are staged. Con-
trol types are:
• C.TYP = 1 (VAV-RAT) and C.TYP = 2 (VAV-S P T)
Both of these configurations refer to standard VAV opera-
tion. If the control is occupied, the supply fan is run con-
tinuously and return-air temperature will be used for both
in the determination of the selection of a cooling mode.
VAV-SPT differs from VAV-RAT only in that during the
unoccupied period, space temperature will be used instead
of return-air temperature to start the fan for 10 minutes
before the return-air temperature is allowed to call out any
mode.
• C.TYP = 3 (TSTAT-MULTI)
This configuration will force the control to monitor the
thermostat inputs to make a determination of mode.
Unlike traditional 2-stage thermostat control, the unit is
allowed to use multiple stages of cooling control and per-
form VAV style operation. The control will be able to call
out a LOW COOL or a HIGH COOL mode and maintain a
low or high cool supply air setpoint.
• C.TYP = 4 (TSTAT-MULTI2)
This control is the same as C.TYP=3.
• C.TYP = 5 (SPT-MULTI)
This configuration will force the control to monitor a
space temperature sensor to make a determination of
mode. Unlike traditional 2-stage space temperature con-
trol, the unit is allowed to use multiple stages of cooling
control and perform VAV style operation. The control will
be able to call out a LOW COOL or a HIGH COOL mode
and maintain a low or high cool supply air setpoint.
• C.TYP = 6 (SPT-MULTI2)
This Control is the same as C.TYP = 5.
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