Carrier 48LC 04 Controls, Start-Up, Operation And Troubleshooting page 17

specific unit wiring diagram and or service manual for details on
how the outdoor fan operates. In general, the outdoor fan will be
on full speed when the compressor is turned on. The control
system can override the speed of the outdoor fan for low ambient
operation. When the Outdoor Air Temperature (Temperatures
→AIR.T →OAT) falls below the Low Ambient ODF Setpoint
(Configuration →COOL →LA.SP) the Low Ambient Outdoor
Fan relay (Outputs →COOL →L.ODF) will be energized. When
this happens the outdoor fan will reduce its speed to the pre-set low
ambient RPM. The ambient must then rise 5_F above LA.SP to
allow full speed on the outdoor fan.
Indoor Fan Smart Staging Control
On direct drive fan units the fan will follow simple control. With
one stage of cooling running, the fan will run the low fan speed.
With 2 stages of cooling running, the fan will run high fan speed.
On belt drive VFD fan units the fan will be controlled as described
below. Refer to the Fan operation section for other details on fan
operation.
The indoor fan speed will change throughout cooling operation
based on cooling demand, run time, supply air temperature, and
refrigerant suction temperature. With only one stage of cooling
running the fan will run at Supply Fan Speed 1 (F.SP1) and then
Supply Fan Speed 2 (F.SP2). With 2 stages of cooling running the
fan will run at Supply Fan Speed 3 (F.SP3) and then Supply Fan
Maximum Speed (FS.MX). The fan will wait the Fan Transition
Time (Configuration →Cooling →FTT) between fan speeds 1 and
2 or 3 and max, unless the supply air overrides it. The supply air
temperature (SAT) can override the FTT if it falls below the
Minimum Supply Air Temperature Upper Level (SAT.U) or if its
trend (SA.TR) anticipates a need for more air. The fan will be
allowed to run F.SP3 if the SAT is limiting second stage cooling.
Maximum Speed (FS.MX) will be allowed too after running F.SP3
for half of FTT.
Any time during cooling after the compressor has been on for 2
minutes, a low refrigerant suction temperature can override the fan
speed to the Supply Fan Maximum Speed (FS.MX). This will
occur if the Sat. Suction Temp A (Temperatures →REF.T
→SST.A) falls below the Fan Low Suction Temp (Configuration
→COOL →SST →FLSU) for one minute. If both cooling stages
are on with the fan at Max speed and the low suction condition
occurs for 1 minute, then the second cooling stage will be
removed. The Fan Low Suction State (Operating Modes →COOL
→LSST) will be set to yes. Cooling stage 2 will be allowed back
on after the Compressor Min Off Time (MOT.C), and the Fan Low
Suction State can be cleared after 5 minutes of running without the
low suction condition. If the suction returns low within the 5 min,
then a stage down of cooling stage 2 will occur again. If this cycle
happens 3 times in a row, the Full Load Lockout (Operating
Modes →COOL →FLLO) will be set to yes and the second
cooling stage will not be allowed back on until the cooling demand
is removed.
Dehumidification Control
Dehumidification operation requires installation and configuration
of either a space relative humidity sensor or a relative humidity
switch input. Space Humidity Switch (Configuration →UNIT
→RH.SW) set to 1 for use of a normally open switch, or 2 for
normally closed switch. The switch is wired to the field connection
terminal board terminals R-2 and HUM. RH Sensor on OAQ Input
(Configuration →UNIT →RH.S) set to Yes for use of a 4 to 20
mA output RH sensor wired to field connection terminal board
terminals LPWR and SPRH (for loop powered). RH Sensor Value
at 4ma (Configuration→AIR.Q→H.4M) sets the % display for a
4mA input from the relative humidity sensor. RH Sensor Value at
20ma (Configuration→AIR.Q→H.20M) sets the % display for a
20mA input from the relative humidity sensor.
IMPORTANT: The HUM terminal on the field connection board
is not wired and requires a isolation relay with gold plated contacts
to wire to MBB J9-5 and 6. The RH sensor input requires the ECB
to be installed if not already.
Dehumidification is a cooling mode function. When using a
humidistat or switch input, the demand for dehumidification is
seen as Space Humidity Switch (Inputs →GEN.I →HUM) being
Low or High. A low value means humidity level is good and a
high value means that dehumidification is needed. When using an
RH sensor, the demand is based on the Space Humidity Sensor
(Inputs →AIR.Q →SP.RH) value compared to the Space RH
Setpoint (Setpoints →RH.SP). If the Space Humidity Sensor
(SP.RH) value is above the Space RH Setpoint (RH.SP), then
dehumidification is needed. If the Space Humidity Sensor (SP.RH)
value is below the Space RH Setpoint (RH.SP) minus the Space
RH Deadband (Setpoints →RH.DB), then dehumidification is no
longer needed. If the unit is configured for space sensor control
(Configuration →UNIT →U.CTL = 3), then the setpoint Dehum
Heat SP Deadband (Setpoints
configuration sets the offset above the heating set point at which a
unit in dehum mode will turn off. This is a protection against over
cooling the space and causing a heat demand. There are three types
of dehum control set by the configuration Dehum Control Type
(Configuration →COOL →DHUM). Dehum Control is factory
defaulted to 0 which is No Control meaning that any dehum
demand is ignored.
NOTE: When there is a dehumidification demand, the economizer
damper position is limited to its minimum damper position
(Operating Mode →ECON →EC.MP).
Max Dehum (DHUM = 1)
When the Dehum Control Type (DHUM) is set to (1) Max dehum,
the control will try to satisfy the dehum demand. The Fan
Transition Time (FTT) will not be utilized nor the Supply Air
Upper Level (SAT.U). The Supply Air Lower Level (SAT.L) limit
will be honored while running the cooling stages.
Suction (FLSU) will be handled per below.
With only a dehum demand, the control will start with 1
cooling at the Supply Fan Speed 1 (F.SP1). When stage 2 is
available it too will be requested leaving the fan at F.SP1. If the
Sat. Suction Temp A (SST.A) falls below the Fan Low Suction
Temp (FLSU) for one minute the fan will step up to Supply Fan
Speed 2 (F.SP2) for one minute. If SST.A still falls below FLSU
for one minute the fan will run at Supply Fan Speed 3 (F.SP3). If
the low suction still occurs, the second cooling stage will be
removed and the fan set back to F.SP1. If the low suction still
persists, then the fan will run at F.SP2 until the low suction alarm
trips out the circuit or the dehum call is satisfied.
With a dehum call and 1 stage of cooling being requested, the
control will run 1 stage of cooling at Supply Fan Speed 1 (F.SP1).
If the Sat. Suction Temp A (SST.A) falls below the Fan Low
Suction Temp (FLSU) for one minute the fan will step the fan to
F.SP2, if it continues, the fan will ramp to Supply Fan Maximum
Speed (FS.MX).
If dehum and max cooling is being requested, the control will run
both cooling stages at Supply Fan Speed 2 (F.SP2). Fan Low
Suction Temp (FLSU) will follow normal cooling operation.
Max Comfort (DHUM = 2)
When the Dehum Control Type is set to (2) Max Comfort, the
control will try to satisfy the demand while minimizing the cold air
dump. The Fan Transition Time (FTT) will not be utilized nor the
Supply Air Upper Level (SAT.U). The Supply Air Lower Level
(SAT.L) limit will be honored while running the cooling stages.
Fan Low Suction (FLSU) will be handled per below.
With only a dehum demand, the control will run 1 stage of cooling
at Supply Fan Speed 1 (F.SP1). If Supply Air Temperature (SAT)
falls below the Comfort SAT Setpoint (Setpoints →CCSP), the fan
speed will be raised to Supply Fan Speed 2 (F.SP2) for one minute
and so on up until Supply Fan Maximum Speed (FS.MX) is
reached or the SAT raises above the Comfort SAT Setpoint
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→RH.HB) applies. This
Fan Low
st
stage of