67
As the capacity requirement begins to decrease, the ma-
chine controls will reduce the unit’s capacity to maintain the
Control Point. If the unit is equipped with Minimum Load
Control, it will not be active until the unit is on its last stage of
capacity.
C.TYP =
3
(TSTAT MULTI) — This configuration will
allow the MBB to monitor the thermostat inputs to make a
determination of supply air temperature. Unlike traditional
2-stage thermostat control, the unit is allowed to perform VAV
style operation using multiple stages of cooling capacity to
attempt to meet the current Control Point (
Run Sta-
tus
o
VIEW
o
CTPT
).
Recommended Applications — This control scheme is rec-
ommended for constant volume or 100% outdoor air applica-
tions. It can be used with or without digital compressors. This
control method is recommended for 38APD,APS025-030 units
with digital scroll option and 38APD,APS040-130 units with
two-stage thermostat control. Minimum Load Control is sup-
ported by this control scheme. Minimum Load Control and
digital compressor operation are not supported simultaneously.
Hardware Requirements
• supply air sensor
• return air sensor or mixed air sensor
• 2-stage thermostat
This control scheme requires a supply air sensor and a return
air sensor or mixed air sensor. In lieu of wiring sensors to the
38AP unit, both values can be communicated via CCN to the
38AP. For information on broadcasting values, see the section
Thermistors on page 28.
Configuration
o
OPT1
o
RAT.T
(RAT Thermistor Type) and
Configuration
o
OPT1
o
SAT.T
(SAT Thermistor Type) must be configured for either
0
(5 k
:
)
or
1
(10 k
:
) type sensors whether they are hard wired or their
values are communicated to the controller.
Required Configurations — Table 27 lists the configurations
required for proper operation.
Recommended Settings — With this Control Type,
CSP.2
should be set to the design Supply Air Temperature.
CSP.1
will depend on the application. The difference between the
default values for
CSP.1
and
CSP.2
is 5° F (2.8° C). In most
cases, the default differential is acceptable, but the application
may require a smaller or larger difference. For example, a face
split coil may a larger differential.
CSP.1
should be set to a
value that allows the unit to operate without rapid cycling.
CSP.1
should be greater than
CSP.2
to allow the unit to
produce a lower supply air temperature when Y2 is made, if
the unit has the available capacity.
Wiring— See Fig. 81.
Sequence of Operation — The MBB monitors the thermostat
inputs to make a determination of Active Set Point (
Run Sta-
tus
o
VIEW
o
SETP
). The control will vary the Active Set
Point based on Y1 and Y2 inputs. When Y1 is closed Cooling
Setpoint 1 (
Setpoints
o
COOL
o
CSP.1
) will be used and when
Y2 is closed Cooling Setpoint 2 (
Setpoints
o
COOL
o
CSP.2
)
will be used as the basis for the Active Set Point,
SETP
. Ther-
mostat inputs can be monitored at the unit’s interface device,
Y1Thermostat Input (
Inputs
o
GEN.I
o
Y.1
) and Y2 Thermo-
stat Input (
Inputs
o
GEN.I
o
Y.2
). With this type of control,
the MBB capacity control routine stages compressor capacity
to attempt to meet the current Control Point (
Run Sta-
tus
o
VIEW
o
CTPT
). The Control Point (
Run Sta-
tus
o
VIEW
o
CTPT
) is the Active Set Point (
SETP
) adjusted
for any temperature reset that is applied. See Temperature
Reset on page 129 for additional information.
For mechanical cooling, the unit’s Control Method (
Con-
figuration
o
OPT2
o
CTRL
) and inputs must allow the ma-
chine to run. See Control Methods on page 60 for additional
information.
Table 27 —
C.TYP=3 (Tstat Multi) Required Configuration
CONFIGURATION MODE
SUBMODE
ITEM
DISPLAY
ITEM DESCRIPTION
COMMENT
OPT1
RAT.T
X
RAT Thermistor Type
Default: 0
Range: 0 to 2
Must be set for appropriate value:
0 = 5 k
:
1 = 10 k
:
2 = None
SAT.T
X
SAT Thermistor Type
Default: 0
Range: 0-2
Must be set for appropriate value:
0 = 5 k
:
1 = 10 k
:
2 = None
OPT2
C.TYP
X
Machine Control Type
Default: 4
Range: 1 to 9
Set Item to 3 (Tstat Multi)
SETPOINTS MODE
COOL
CSP.1
XX.X
Cooling Setpoint 1
Range: 40.0 to 80.0 F (4.4 to 26.7 C)
Default: 60.0 F (15.6 C)
Set for desired Supply Air Temperature
with Y1 input.
CSP.2
XX.X
Cooling Setpoint 2
Range: 40.0 to 80.0 F (4.4 to 26.7 C)
Default: 55.0 F (12.8 C)
Set for desired Supply Air Temperature
with Y2 input. Should be lower than
CSP.1
