37
The A Series
Comfort
Link™ control offers two basic con-
trol approaches to mechanical cooling. Constant volume for 2
stages of cooling and VAV for multiple stages of cooling. In ad-
dition to these methods of control, the A Series
Comfort
Link
control offers the ability to run multiple stages of cooling for
either a space temperature sensor or thermostat 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 technique
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: Configuring 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
→
UNIT
→
C.TYP
) —
The most fundamental cooling control configuration is located
under
Configuration
→
UNIT
.
This configuration defines the technique and control source
responsible for selecting a cooling mode and in determining 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 ten 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
COOL or a HIGH COOL mode and maintain a low or high
cool supply air set point.
•
C.TYP
= 4 (TSTAT – 2 STG)
This configuration will force the control to monitor the ther-
mostat 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 set point.
•
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 pre-
served by the download process of the new software. The fol-
lowing configurations apply to all machine control types
(
C.TYP
) except 4 and 6. These configurations are located at the
local display under
Configuration
→
UNIT
.
See Table 44.
Table 44 — Machine Dependent Configurations
*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.
SET POINTS — The set points for both cooling and heating
are located at the local display under
Setpoints
.
See Table 45.
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.R.
See Table 46.
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
• 1 = SPT RESET
Space temperature will be used as the reset control variable
along with both
RTIO
and
LIMT
in the calculation of the
final amount of reset to be applied (
Inputs
→
RSET
→
SA.S.R
).
• 2 = RAT RESET
Return-air temperature will be used as the reset control vari-
able along with both
RTIO
and
LIMT
in the calculation of
the final amount of reset to be applied (
Inputs
→
RSET
→
SA.S.R
).
• 3 = 3RD PARTY RESET
The reset value is determined by a 4 to 20 mA third party
input. An input of 4 mA would correspond to 0º F reset. An
input of 20 mA would correspond to 20º F reset. Configur-
ing the control for this option will cause
RES.S
to become
enabled automatically with the CEM board. To avoid
alarms make sure the CEM board and third party input are
connected first before enabling this option.
Reset Ratio (
RTIO
) — This configuration is used when
RS.CF
is set to 1 or 2. For every degree that the controlling
temperature (space/return) falls below the occupied cooling set
point (
OCSP
), the calculated value of the supply air reset will
rise by the number of degrees as specified by this parameter.
Reset Limit (
LIMT
) — This configuration is used when
RS.CF
is set to 1 or 2. This configuration places a clamp on the
amount of supply air reset that can be applied.
EDT 4-20 mA Reset Input (
RES.S
) — This configuration is
automatically enabled when
Configuration
→
EDT.R
→
RS.CF
is set to 3 (third party reset).
COOLING CONFIGURATION — Relevant configurations for
mechanical cooling are located at the local display under
Configuration
→
COOL
.
See Table 47.
ITEM
EXPANSION
RANGE
CCN
POINT
DEFAULTS
UNIT
UNIT CONFIGURATION
SIZE
Unit Size (20-60)
20-60
UNITSIZE
*
Summary of Contents for WEATHERMAKER 48AJ020
Page 95: ...95 Fig 13 Typical Main Control Box Wiring Schematic A48 7787 ...
Page 96: ...96 TO NEXT PAGE Fig 14 Auxiliary Control Box Wiring Schematic A48 7294 ...
Page 98: ...98 Fig 15 Typical 2 Stage Gas Heat Wiring Schematic Size 051 and 060 Units Shown A48 6866 ...
Page 102: ...102 TO NEXT PAGE Fig 18 Typical Power Schematic Size 051 and 060 Units Shown A48 7298 ...
Page 104: ...104 Fig 19 Controls Option Wiring Schematic A48 7810 ...
Page 105: ...105 Fig 20 Small Chassis Component Location Size 020 035 Units A48 7301 ...
Page 106: ...106 Fig 21 Large Chassis Component Locations Size 036 060 Units A48 7302 ...