64
pushed. This item has a range of 0 to 4 hours and should be set
to the limit desired for the override period. See Table 24.
Pressing the override button on the Space Temperature Sen-
sor will initiate an override period. The override button must
be pressed for 2 to 4 seconds for the control to acknowledge the
call. The control will ignore a momentary press of the override
button. However, if the override button is held for longer than 4
seconds, a Space Temperature Thermistor Failure alarm will be
generated. The number of hours in the override time period
will be displayed in Time Clock
OVR
OVR.T (Timed
Override Hours) and will count down as the time period pro-
gresses. See Table 23.
Once a non-zero value has been entered, the unit will re-
sume an occupied period for the duration of the time pro-
grammed. The number of hours in the override time period will
be displayed in OVR.T and will count down as the time period
progresses. This value cannot be changed until the override pe-
riod has expired or is cancelled. The override time period can
be cancelled by changing the OVR.T value to 0. This can be
done at the unit’s interface device or through CCN communi-
cations by writing to the point OVR_EXT.
Table 24 — Space Temperature Override Required
Configuration
Timed Override from CCN — A timed override period can be
initiated through CCN communications by writing to the point
OVR_EXT. This point has a range of 0 to 4 hours and should
be set for the desired amount of time.
The number of hours in the override time period will be dis-
played in Time Clock
OVR
OVR.T (Timed Override
Hours) and will count down as the time period progresses. See
Table 23.
Once a non-zero value has been entered, the unit will re-
sume an occupied period for the duration of the time pro-
grammed. The number of hours in the override time period will
be displayed in OVR.T and will count down as the time period
progresses. This value cannot be changed until the override pe-
riod has expired or is cancelled. The override time period can
be cancelled by changing the OVR.T value to 0. This can be
done at the unit’s interface device or through CCN communi-
cations by writing to the point OVR_EXT.
CCN CONTROL — With the control method set to CCN
Control, CTRL=3 (CCN), an external CCN device controls the
On/Off state of the machine. This CCN device forces the point
CHIL_S_S between Start/Stop to control the unit.
Under normal operation, Run Status
VIEW
STAT
(Control Mode) will be 1 (Off Local) when the Enable/Off/Re-
mote Control switch is in the Off position or in the Remote
Control position with the remote external contacts open. With
the Enable/Off/Remote Control switch in the Enable position
or in Remote Control position with the remote external con-
tacts closed, the Control Mode will be 2 (Off CCN) when the
CHIL_S_S variable is “Stop.” Similarly, the control mode will
be 6 (On CCN) when the CHIL_S_S variable is “Start.” If the
machine is ON, Control Type Configuration
OPT2
C.TYP=5 (SPT Multi) is used, and the space temperature is sat-
isfied, the Control Mode 9 (SPT Satisfied) will be displayed.
Units controlled via communications by a separate third-
party building automation system through a translator or UPC
Open Controller must be set to CCN Control, CTRL=3. If the
unit is to be monitored only via communications, CTRL=3
(CCN Control) is not required.
Emergency Stop
— A controls feature exists to shut down the
machine in the event of an emergency. Writing to the CCN
Point EMSTOP, the command “EMSTOP” will force the
machine to stop all mechanical cooling immediately and shut
down. While this feature is enabled, the Control Mode Run
Status
VIEW
STAT=4 (Emergency) will be displayed.
For the machine to operate normally, the EMSTOP point value
should be “ENABLE.”
Capacity Control — When mechanical cooling is
required, the Main Base Board (MBB) can control the unit
capacity by staging compressors and controlling the digital
scroll compressor operation. The control also checks on vari-
ous other operation parameters in the unit to make sure that
safeties are not exceeded and the compressors are reliably
operated.
The ComfortLink control system offers two basic control
approaches to mechanical cooling: constant volume operation
for 2 stages of cooling, or variable air volume (VAV) operation
for multiple stages of cooling. In addition to these methods of
control, the ComfortLink control offers the ability to run multi-
ple stages of cooling from a space temperature sensor, thermo-
stat, return air temperature, or directly from a 4 to 20 mA sig-
nal. The Control Type (Configuration
OPT2
C.TYP) de-
termines the selection of the type of cooling control as well as
the method for selecting a cooling capacity input.
C.TYP = 1 (VAV) — This configuration is the standard VAV
operation. With this control type, the MBB capacity control
routine stages compressor capacity to attempt to meet the cur-
rent Control Point (Run Status
VIEW
CTPT).
Recommended Applications
— This control scheme is rec-
ommended for VAV applications with a single 38AP unit
matched with a single air handler. It can be used for 38AP
units with or without digital compressors; however, better tem-
perature control will be achieved with the digital compressor
option. Minimum Load Control is supported by this control
scheme. Minimum Load Control and digital compressor oper-
ation are not supported simultaneously.
Hardware Requirements
• supply air sensor
• 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 Thermistors section on page 28.
The Return Air Thermistor (Configuration
OPT1
RAT.T)
and Supply Air Thermistor (Configuration
OPT1
SAT.T)
must be configured for either 0 (5,000 :) or 1 (10,000 :) type
sensors whether they are hard-wired or their values are com-
municated to the controller.
Required Configurations
— Table 25 shows configurations
required for proper operation.
Recommended Settings
— CSP.1 should be set to the design
supply air temperature (SAT).
Wiring
— See Fig. 80.
TIME CLOCK MODE
SUBMODE ITEM DISPLAY
ITEM
DESCRIPTION
COMMENT
OVR OVR.L X
Override Time
LImit
Default: 0
Range: 0 to 4
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