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When
Cooling Control —
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 addition, the Com-
fortLink control system supports the use of an optional mini-
mum load hot gas bypass valve (MLV) that is directly
controlled by the ComfortLink control system. This provides
an additional stage of capacity as well as low load coil freeze
protection. The control also integrates the use of an econo-
mizer with the use of mechanical cooling to allow for the
greatest 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
supply 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
compressors (B1,B2). There may be a minimum load valve
(MLV), which, if present, is only associated with circuit A. The
decision as to which compressor should be turned on or off is
decided by the compressor's availability followed by a pre-
ferred 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
installed 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
volumes for VAV operation. Refer to the section on static pres-
sure 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
The most important cooling control configuration is located
under Configuration
UNIT.
This configuration defines the method and control source
responsible for selecting a cooling mode. The configuration
also determines the method by which compressors are staged.
Control types are:
• C.TYP = 1 (VAV-RAT) and C.TYP = 2 (VAV-SPT)
Both of these configurations refer to standard VAV opera-
tion. If the control is occupied, the supply fan is run continu-
ously 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 ther-
mostat inputs to make a determination of mode. Unlike tra-
ditional 2-stage thermostat control, 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
mechanical
cooling
is
UNIT
C.TYP) —
COOL or a HIGH COOL mode and maintain a low or high
cool supply air setpoint.
• C.TYP = 4 (TSTAT-2 STG)
This configuration will force the control to monitor the
thermostat inputs to make a determination of mode.
• C.TYP = 5 (SPT-MULTI)
This configuration will force the control to monitor a space
temperature sensor to make a determination of mode. Un-
like traditional 2-stage space temperature 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 = 6 (SPT-2 STG)
This configuration will force the control to monitor the
space temperature sensor to make a determination of mode
and allow two stages of cooling.
MACHINE DEPENDENT CONFIGURATIONS — Some
configurations are linked to the physical unit and must not be
changed. The configurations are provided in case a field re-
placement of a board occurs and the settings are not preserved
by the download process of the new software. The following
configurations apply to all machine control types (C.TYP) ex-
cept 4 and 6. These configurations are located at the local
display under Configuration
Table 33 — Machine Dependent Configurations
ITEM
EXPANSION
UNIT
UNIT CONFIGURATION
SIZE
Unit Size (20-60)
RFG.T REFRIG
CND.T CND HX TYP
*Dependent on unit.
Unit Size (SIZE) — There are several unit sizes (tons) for the
A Series control. Make sure this configuration matches the size
called out by the model number of the unit. This is important as
the cooling stage tables are directly determined based on this
configuration.
Refrigerant Type (RFG.T) — This configuration specifies the
type of refrigerant used in the unit. Configuration RFG.T is set
to 0 if the refrigerant used is R-22. Configuration RFG.T is set
to 1 if the refrigerant used is R-410A. Make sure this configu-
ration matches the refrigerant called out by the model number
of the unit.
Condenser Type (CND.T) — This configuration specifies the
type of condenser installed in the unit. Configuration CND.T is
set to 0 if the condenser is a round tube, plate fin coil (RTPF).
Configuration CND.T is set to 1 if the condenser is a micro-
channel heat exchanger coil (MCHX). Make sure this configu-
ration matches the condenser type called out by the model
number of the unit.
SETPOINTS — The setpoints for both cooling and heating
are located at the local display under Setpoints. See Table 34.
SUPPLY AIR RESET CONFIGURATION — Supply Air
Reset can be used to modify the current cooling supply air set-
point. Supply Air Reset is applicable to control types, C.TYP =
1, 2, 3, and 5. The configurations for reset can be found at the
local display under Configuration
EDT Reset Configuration (RS.CF) — This configuration ap-
plies to several machine control types (Configuration
UNIT
C.TYP = 1,2,3, and 5).
• 0 = NO RESET
No supply air reset is in effect.
32
UNIT. See Table 33.
CCN
RANGE
DEFAULTS
POINT
20-60
UNITSIZE
*
0-1
REFRIG_T
*
0-1
COILTYPE
*
EDT.R. See Table 35.
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