Cooling Operation - Carrier 48LC Series Controls, Start-Up, Operation And Troubleshooting

Indoor (Supply) Fan Maximum Speed
(MAXIMUM IDF SPEED)
Max speed is the highest fan speed allowed. This is typically 100%
when pulleys are set to deliver design CFM to the space per job
requirement. Most safety conditions for the unit will override the
fan speed to this to help protect the unit.
Ventilation Indoor Fan Speed (VENT IDF SPEED)
This configuration defines the fan speed used in Ventilation
(fan- -only) mode. Ventilation mode is when the supply fan is
running, but there is no demand for heating or cooling. In
thermostat mode, this is with just a G call. In space sensor control,
this is when the unit is Occupied mode and the indoor fan is
configured to always run while occupied (OCCUPIED FAN?). If
the indoor fan is configured for intermittent fan (OCCUPIED
FAN? = No), the Mode will be off instead of Ventilation and the
fan will not run unless a heating or cooling mode is needed. During
the unoccupied period, the fan will always operate intermittently.
The economizer damper will adjust its position based on how far
away this speed is from max speed for ventilation.
IMPORTANT: It is important that the ventilation rate is checked after
setting this speed to verify that the unit can properly ventilate the space
per requirements. Adjusting this configuration or the economizer
minimum setting curve should be performed to meet job requirements.
Heating Indoor Fan Speed (HEATING IDF SPD)
This configuration defines the fan speed used when in heating
mode and running heat. On units equipped with Gas heat (UNIT
TYPE OF HEAT), this heat speed will be delayed on based on the
IGC's fan on call (IGC FAN REQUEST). Once the IGC request
the fan the fan will run what this heating speed configuration is set
for until heating is ended. On units configured for Electric heat
(UNIT TYPE OF HEAT) and configured for Preheat without the
fan (PREHEAT W/O IDF), this heat speed will be delayed on
based on the Preheat fan delay time (PREHEAT FAN DELAY).
Once this preheat time has expired or not configured for preheat,
the fan will run at this heat speed while heat is on.
Free Cooling Indoor Fan Speed (FREE COOL IDF SPD)
This configuration defines the initial fan speed used when in Free
Cooling. Refer to the Economizer Controls Operation section for
details on free cooling. The fan will stay at this configured speed
whenever only the damper is being used for free cooling. If the
damper is at 100% for 5 minutes the fan will ramp to the high
cooling speed. It is locked there until the actual damper position
falls below 75% at which time it will ramp back down to this
configured speed.
Low Cooling Indoor Fan Speed (LOW COOL IDF SPD)
This configuration defines the fan speed used when only one stage
mechanical cooling is being performed.
Medium Cooling Indoor Fan Speed (MED COOL IDF SPD)
This configuration defines the fan speed used when only second
stage mechanical cooling is being performed.
High Cooling Indoor Fan Speed (HIGH COOL IDF SPD)
This configuration defines the fan speed used when third (full load)
stage mechanical cooling is being performed. When performing
integrated cooling with the economizer this speed will be used. When
only free cooling with a high cool demand, this speed will be used.

Cooling Operation

The 48/50LC unit's cooling operation consists of: demand and
mode determination, staging request to satisfy the demand, and
handling a request with the unit's resources. These resources can
include compressors, Humidi- -MiZer
fan speed based on options. This section covers mechanical
cooling. For economizer free cooling, refer to the Economizer
Operation section (starting on page 24).
For Humidi- -MiZer system operation, refer to the Optional
Humidi- -MiZer Dehumidification System section (see page 19).
R
system, an economizer, and
Cooling Mode Control
The cooling HVAC mode (OPERATING MODE) has 9 different
operating sub modes (SUBMODE): ECON FREE COOLING,
UNOCC. FREE COOL, MECH. COOLING, ECON/MECH
COOLING, DEHUMIDIFICATION, DEHUM/MECH COOLING,
DEHUM PREVENTED,
SHUTTING COOL OFF. These are all part of a general cooling
mode and resemble the specific type of cooling that is 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.
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 or dehumidification demand
(Y1, Y2, Y3, space cool demand, or humidity demand). The unit will
remain in cooling for at least one minute or until any of the above
conditions turn false. The cooling mode does not officially end until
the compressor is off and the fan off delay has expired.
Cooling Staging Control
Once the unit is in a cooling mode, determine what the demand is
and how to satisfy it. If an economizer is installed and can be used
for cooling (OK TO USE FREE COOLING? = 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?
(OK TO USE COMPS?) will be set to yes when the outdoor
temperature (OUTDOOR AIR TEMP) is above the Circuit A
Lockout temperature (CIR.A LOCKOUT OAT) and the Circuit A
is not locked out for diagnostic reasons (CIRCUIT A LOCKOUT).
Based on the unit control configuration, requested cooling stages
(REQ. COOL STAGES) will be determined then passed to
compressor control to actually add the cooling stages.
There are two ways of requesting stages when thermostat control is
enabled, Traditional thermostat control or adaptive control.
Traditional thermostat control is used if set for non- -adaptive
thermostat (ADAPTIVE TSTAT = NO) and the unit cannot use the
economizer for free cooling. If set for adaptive thermostat
(ADAPTIVE TSTAT = YES) or any time the economizer is
available for free cooling, the unit will use adaptive control for
staging.
When configured for Space sensor or RAT control (UNIT
CONTOL TYPE) the unit will use adaptive control for staging.
With either staging method there are two supply air temperature
limits that apply, one restricts more cooling stages and the other
will remove cooling stages. If at any time the Supply- -Air
Temperature (SUPPLY AIR TEMP) falls below the Minimum
Supply Air Temperature Upper Level (UPPER MIN SAT), the
requested stages will not be allowed to increase. If at any time the
SAT falls below the Minimum Supply Air Temperature Lower
Level (LOWER MIN SAT), the requested stages will be reduced
by one. If these SAT limits are configured so that they are too close
together, the last stage might cycle rapidly, slowed only by its
minimum on and off- -time requirements.
Adaptive Control
Stage timers and Supply air trend apply when determining the
request for stages. The first request (REQ. COOL STAGES =1)
comes immediately when starting the staging process. The Cool
Stage Increase Time (COOL STAGEUP TIME) has to expire and
the Supply- -Air Trend (SUPPLY AIR TREND) has to be above
the cooling supply air trend level (COOL SATTREND LEV)
before another stage can be added. Requested stages will only be
allowed to increase as the actual system demand allows
(DEMAND). A "LOW COOL" demand will only allow one
requested stage, "MED COOL" two stages, and "HIGH COOL" 3
stages. The requested stages will be reduced if the cooling demand
is lowered or dropped completely, or if the supply air falls below
the lower level (LOWER MIN SAT).
17
COOLING PREVENTED, and