Carrier 48LC 04 Controls, Start-Up, Operation And Troubleshooting page 16

Free Cooling, and Dehumidification. These are all part of a general
cooling mode and resemble the specific type of cooling that being
performed at any given time. All types of cooling are still performed
under the general cooling function, and the expanded text is for user
reference only. The control will display if it is ok to select the
cooling mode (Operating Modes →COOL →OK.CL= Yes).
Thermostat Control
For the unit to enter cooling mode, three things must be true: the
indoor fan must be ok to use, the mode changeover time guard
must be expired, and there must be a cooling demand (Y1, Y2, or
dehum demand). The unit will remain in cooling until the cooling
demand is dropped or if any of the above conditions turn false. If
only a dehum demand exists and a heat demand (W1, W2) occurs,
the unit will end cooling. The cooling mode can not officially end
until the compressor is off.
Space Sensor Control
For the unit to enter cooling mode, four things must be true: the
indoor fan must be ok to use, the mode changeover time guard
must be expired, the unit must have a valid space temperature, and
there must be a cooling or dehum demand. The unit will remain in
cooling for at least one minute and until the demand is dropped or
if any of the above conditions turn false. If only a dehum demand
exists and the heat demand becomes greater than the Dehum Heat
Setpoint Deadband (Setpoints →RH.HB), the unit will end
cooling. The cooling mode can not officially end until all
compressors are off.
Cooling Staging Control
Once the unit is in a cooling mode, it must decide what the demand
is and how to satisfy. If an economizer is installed and can be used
for cooling (Operating Modes →COOL →OK.EC= Yes), the unit
will use it first (see economizer section for its operation). If the
economizer cannot be used or additional cooling is needed, a
mechanical cooling check is performed. OK to use Compressors?
(Operating Modes →COOL →OK.MC), will be set to yes when
the compressor is enabled and not locked out. Based on the unit
control configuration, requested cooling stages (Run Status
→COOL →REQ.C) will be determined then passed to compressor
control to actually add the cooling stages.
Thermostat Control
There are two ways of requesting stages when thermostat control is
enabled, Traditional Thermostat control or Adaptive control.
Traditional Thermostat control is used if the Thermostat Control
Type (T.CTL) is set to 1, 2, or 3 and the unit cannot use the
economizer for free cooling. If Thermostat Control (T.CTL) is set
for 0 or any time the economizer is available for free cooling, the
unit will use Adaptive control for staging.
T.CTL = 0 (Adaptive Control)
Stage timers, Supply air trend, and supply air temperature limits
apply when determining the request for stages. The first request
(REQ.C=1) comes immediately when the Y1 input is active. The
Cool Stage Increase Time (Configuration →COOL →C.INC) or
the Cool Stage Decrease Time (Configuration →COOL
→C.DEC) has to expire before another stage can be added or a
stage can be subtracted. The Supply-Air Trend (Operating Modes
→COOL →SA.TR) decides if the next stage can be requested or
should be subtracted based on the Y2 input status. If the Y1 and
Y2 inputs are dropped, the supply air trend is not considered
because cooling is no longer needed. If at any time the Supply-Air
Temperature (SAT) falls below the Minimum Supply Air
Temperature Upper Level (Configuration →COOL →SAT
→SAT.U), the requested stages will not be allowed to increase. If
at any time the SAT falls below the Minimum Supply Air
Temperature Lower Level (Configuration →COOL →SAT
→SAT.L), the requested stages will be reduced by one without
honoring C.DEC. If SAT.L and SAT.U are configured so that they
are close together, the last stage might cycle rapidly, slowed only
by its minimum on and off-time requirements.
T.CTL = 1 or 2 (1 Stage Y1 or 2 stage Y1)
Stage timers, Supply air trend, and supply air temperature limits do
not apply when determining the request for stages. Request staging
will follow the thermostat inputs directly. Y1 will request one
stage. Y2 will request all stages.
T.CTL = 3 (Digital)
Stage timers, Supply air trend, and supply air temperature limits do
not apply when determining the request for stages. Request staging
will follow the thermostat inputs directly. Y1 will request one
stage. Y2 will request two stages. Y1 and Y2 will request all
stages.
Space Sensor Control
Space sensor staging control is an adaptive anticipation control that
weighs the actual space demand against the trend of that demand
and the trend of the supply air. It also honors stage time guards and
supply air limits. The demand for cooling in the space is displayed
as the Cooling Demand (Run Status →COOL →DMD.C). The
control tries to anticipate the change in the space because of its
current stage status. This anticipation is based on the Supply-Air
Trend (Operating Modes →COOL →SA.TR) and the Cool
Demand Trend (Operating Modes →COOL →TRD.C). These
trends will show the control how the space is reacting to the current
running conditions and help it decide when to add or remove one
stage from the requested stages. The Cool Stage Increase Time
(Configuration →COOL →C.INC) or the Cool Stage Decrease
Time (Configuration →COOL →C.DEC) has to expire before
another stage can be added or a stage can be subtracted. If at any
time the Supply-Air Temperature (SAT) falls below the Minimum
Supply Air Temperature Upper Level (Configuration →COOL
→SAT →SAT.U), the requested stages will not be allowed to
increase. If at any time the SAT falls below the Minimum Supply
Air Temperature Lower Level (Configuration →COOL →SAT
→SAT.L), the requested stages will be reduced by one without
honoring C.DEC. If SAT.L and SAT.U are configured so that they
are close together, the last stage might cycle rapidly, slowed only
by its minimum on and off-time requirements.
Compressor Control
The compressor control works hand and hand with the staging
control. As the staging control request stages, the compressor
control determines what is available or running and tries to provide
stages for what is requested. The availability of the compressor or
loader depends on time guards, circuit diagnostics, and outdoor
temperature. The Circuit A Lockout Temp (Configuration
→COOL →CA.LO) configuration set the outdoor temperature in
which the compressor is allowed to run down to. Any time the
outdoor ambient falls below 10 degrees, the loader will be locked
on when the compressor is turned on. The outdoor ambient must
then rise above 15 degrees before the compressor will be allowed
to run without the loader. Timeguard A (Run Status →COOL
→TG.A) and Timeguard Loader (Run Status →COOL →TG.L)
display the time the compressor or loader has before it is available
for use. Circuit diagnostic tests are performed during operation
which may or may not allow the compressor or loader to be used.
The available stages at any given time are displayed as Available
Cooling Stages (Run Status →COOL →AVL.C). The actual
stages running at any given time are displayed as Actual Cooling
Stages (Operating Modes →COOL →ACT.C). Compressor A
(Run Status →COOL →CMP.A), and Circuit A Loader (Run
Status →COOL →LDR.A) are displayed on when the respective
output is turned on. There are time guards to protect the
compressor, Compressor Min On Time (Configuration →COOL
→MRT.C) and Compressor Min Off Time (Configuration
→COOL →MOT.C) apply before the compressor or loader can be
turned back on or turned off.
Outdoor Fan Control
The outdoor fan is controlled electromechanically with the
compressor contactor, not directly by the control system. Refer to
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