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

control if the System Mode (SYS) status is enabled. The fan will
remain on if compressors or heat relays are ever stuck on. If
configured for fan status switch (FN.SW) and Shut Down on IDF
Failure is enabled (Configuration →UNIT →IDF.F = Yes), the
fan and unit will be shutdown without delay on alarm. Fan off
delays are honored when exiting specific HVAC modes. The
Fan-off Delay delays are as follows: Mech Cool (Configuration
→COOL →FOD.C), Elect Heat (Configuration →HEAT
→FOD.E), and Gas Heat (Configuration → HEAT →FOD.G).
Direct Drive Units (FTYP = ECM)
Direct Drive ECM fan units can operate with two or three speeds,
set by the number of fan speeds configuration point (NSPD). Low
Speed and High speed are standard unit speeds, and the Ventilation
rd
Speed is the 3 optional speed. These speeds are controlled by the
relays on the main base board (MBB). Indoor Fan Speed Relay 1
(Outputs →FANS →IDF1) controls the low speed command;
Indoor Fan Speed Relay 2 (Outputs →FANS →IDF2) controls
the high speed command; and Indoor Fan Speed Relay 3 (Outputs
→FANS →IDF3) controls the optional vent speed command. The
actual speeds are set by the motor tap in which they are wired to.
For only 2 speed units (NSPD = 2), the vent speed (IDF.3) will not
be used, instead the low speed output will be used during the
ventilation times. Refer to the heating or cooling operation sections
for details on when the fan changes speed, but general operation is
explained below.
Thermostat Control
In thermostat mode, the fan will run vent speed when only the fan
request G in ON. If a cooling request Y1 is ON the fan will be at
low speed. If the cooling request Y2 is ON the fan will be at high
speed. If a heating request W1 or W2 is ON, the fan will run high
speed. If the G call is dropped or was never on with an Y1, Y2,
W1, or W2 call; the fan will turn off after a configurable time delay
with respect to the HVAC mode that is ending.
Space Sensor Control
In Space Sensor mode, the fan will run vent speed if the unit is in
Occupied mode and the indoor fan is configured to always run
while occupied (Configuration →I.FAN →OC.FN = YES). If the
indoor fan is configured for intermittent fan (OC.FN = No), the fan
will only be on at low or high speed when there are cooling,
heating, or dehumidification running; or if there is an air quality
demand. In general, the fan will run low speed with part load
cooling and high speed any other time. During the unoccupied
period, the fan will operate intermittent. With intermittent fan, the
fan will turn off after a configurable time delay with respect to the
HVAC mode that is ending.
Belt Drive VFD Units (FTYP = LEN VFD)
Belt drive fan units are equipped with a Variable Frequency Drive
(VFD), which is powered direct from the distribution block and is
always on with power applied. The VFD communicates on the
Local Equipment Network (LEN) bus. When the thermostat or
space sensor control conditions require the fan, the control will
command the VFD to the desired speed with the Commanded Fan
Speed (Outputs →FANS →F.SPD) point. Feedback from the
VFD can be reviewed in the Supply Fan VFD Menu (Run Status
→S.VFD). Refer to the VFD Major Component section for more
information on the VFD (see page 56).
There are 5 speeds that the indoor fan will run at based on the
running mode and demand for conditioning. The five configurable
speeds are:
Supply Fan Maximum Speed (Configuration →I.FAN →FS.MX)
Supply Fan Speed 1 (Configuration →I.FAN →F.SP1)
Supply Fan Speed 2 (Configuration →I.FAN →F.SP2)
Supply Fan Speed 3 (Configuration →I.FAN →F.SP3)
Fan Speed – Ventilation (Configuration →I.FAN →FS.VN).
Fan speed is always calculated by evaluating the current applicable
conditions. Each fan speed "mode" is evaluated independently, and
the highest requested fan speed is used. When first ramping up
from 0%, the fan will run at max speed (FS.MX) for 1 minute.
Refer to the speed configurations below for an overview of usage;
refer to other specific operating sequences for more details on fan
operation during the corresponding mode.
Supply Fan Maximum Speed (FS.MX)
Max speed is the highest fan speed allowed. This is typically 100%
as 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. In free cooling after the
damper has been at max for 5 minutes, the fan will be set to max
before mechanical cooling can be used and locked at max while
damper is 100% and mechanical cooling is on. With a heating
demand, the fan will always run at this speed. When in an IAQ
override condition the fan will run at this speed. When the IAQ
override condition is cleared the speed will go to the next
commanded speed.
Supply Fan Speed 1, 2, and 3 (F.SP1, F.SP2, and F.SP3)
These configurations define the intermittent fan speeds used during
cooling. Supply Fan Speed 2 (F.SP2) is pre set to the optimum
energy efficiency part load speed. Changing this might affect the
overall efficiency of the unit. Supply Fan Speed 1 and 3 (F.SP1
and F.SP3) are pre set to transition the fan during cooling stage up,
and to aid in dehumidification. These 2 speeds can be adjusted in
the field to optimize dehumidification, load balancing, or
efficiency.
Fan Speed - Ventilation (FS.VN)
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 (Configuration →I.FAN
→OC.FN = YES). If the indoor fan is configured for intermittent
fan (OC.FN = No), the fan will be off instead of this speed during
ventilation. The economizer damper will adjust its position based
on how far away this speed is from max speed.
IMPORTANT: It is important that the ventilation rate is check 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.
Traditional Fan Operation
On units with a belt drive VFD, traditional fan operation can also
be selected. When Smart Fan Control (Configuration → I.FAN →
SMT.F) is set to NO, the fan will operate with simple logic and
run the fan as an electromechanical unit would. When in
ventilation mode, the fan will run at the Fan Speed – Ventilation
(FS.VN) fan speed. When cooling requests the fan, the fan will run
at Supply Fan Speed 2 (F.SP2). Supply Fan Maximum Speed
(FS.MX) will be active anytime 2 cooling stages are requested or
running. In free cooling the fan will run at F.SP2 until the damper
is 100% for 4.5 minutes when the fan will ramp to FS.MX. When
heating request the fan, the fan will run at FS.MX. Advanced
dehumidification function will not be allowed to run. The fan will
still honor respective off delays.

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 compressor, a loader, an economizer, and fan speed based
on options. This section covers mechanical cooling. For
economizer and dehumidification refer to their respective sections.
In general, the unit enters a cooling mode based on a demand,
decides how to satisfy the demand, executes its plan, and then
leaves the cooling mode.
Cooling Mode Control
The cooling HVAC mode (Run Status →MODE →HVAC=3) has
4 different expandable texts: Cooling, Free Cooling, Unoccupied
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