Carrier 48LC Series Controls, Start-Up, Operation And Troubleshooting page 23

at any given time. All types of heating are still performed under the
general heating function, and the expanded text is for user
reference only.
For the unit to be allowed to enter the heat 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 heating demand. The unit
will remain in heating for at least one minute and until the demand is
dropped or if any of the above conditions are false. The heating mode
does not officially end until all heat stages are off, the fan off delay has
expired, and the IGC fan request is dropped.
Supply- - Air Temperature Sensor (SAT) Heat Mode
The SAT Heat Mode Sensing (SAT DURING HEAT?) informs the
unit that the supply air sensor has been relocated downstream of the
heat section. This configuration affects the Supply Air Temperature
(SUPPLY AIR TEMP) value displayed as listed below.
When SAT DURING HEAT? is disabled, the Supply Air
Temperature (SUPPLY AIR TEMP) value on the SystemVut
display and the network will hold a zero when heat outputs come
ON and for 5 minutes after. The default SAT sensor location is at
the fan inlet, upstream of the heat section.
When SAT DURING HEAT? is enabled, the Supply Air Temperature
(SUPPLY AIR TEMP) sensor reading is displayed at the SystemVu
controller and network during heating mode. This setting should only
be used if the original SAT sensor wires are removed from the Main
Base Board (MBB) and replaced by an accessory SAT sensor located
in the supply duct downstream of the heat section.
Heating Staging Control
Once the unit is in a heating mode, it determines what the demand
is and how to satisfy it. Requested Heating Stages (REQ. HEAT
STAGES) will be determined then passed to heat control to
actually add the heating stages. To request stages the number of
heat stages (HEATING STAGE QTY) must be greater than zero.
As a gas unit this will be set in the factory, however 50LC units
may have heat installed as accessories. If the Outdoor Air
Temperature (OUTDOOR AIR TEMP) is greater than the Heating
Lockout Temp (HEAT LOCKOUT OAT), all the heat stages will
be locked out (HEAT LOCKOUT).
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). If set for adaptive thermostat
(ADAPTIVE TSTAT = YES), 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 then two supply air
temperature limits, the Maximum SAT Lower Level (LOWER
MAX SAT) the Maximum SAT Upper Level (UPPER MAX SAT).
Any time the supply air temperature rises above lower level the
heat staging will be limited to what is currently on and no
additional stages will be added until the supply air temperature falls
back below the lower level. If the supply air temperature rises
above the upper level, then heating will be reduced by removing
one stage. That stage will not be added again until the Supply Air
Temperature falls below the lower level. If the supply air
temperature stays above the upper level, then another stage will be
removed. If the upper and lower levels are configured so that they
are close together, the last stage of heat 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. HEAT STAGES =1)
comes immediately when starting the staging process. The Heat
Stage Increase Time (HEAT STAGEUP TIME) has to expire and
the Supply- -Air Trend (SUPPLY AIR TREND) has to be above
the Heating supply air trend level (HEAT 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 HEAT" will only allow one requested stage
and "HIGH HEAT" 2 stages. The requested stages will be reduced
if the heating demand is lowered or dropped completely, or if the
supply air falls below the lower level (LOWER MIN SAT).
Traditional Thermostat Control
Stage timers and Supply air trend do not apply when determining
the request for stages. Request staging will follow the thermostat
inputs directly. "LOW HEAT" will request one stage. "HIGH
HEAT" will request 2 stages.
Heat Relay Control
The heat relay control is responsible for energizing or de- -energizing
the heat stage relays and works hand and hand with the staging
control. As the staging control requests stages, the heat relay control
determines what actual heat relays are available or energized and tries
to provide stages for what is requested. The availability of heat relays
depends on the heat installed, how many stages, and time guards. The
Number of Heat Stages (HEATING STAGE QTY) configuration tells
the control how many heat relays can be used. Heat Stage 1Timeguard
(HEAT 1 TIMEGUARD) and Heat Stage 2 Timeguard (HEAT 2
TIMEGUARD) display the time a respective heat relay has before it
can change state. The available stages at any given time are displayed
as heat 1 available and heat 2 available (HEAT 1 AVAILABLE and
HEAT 2 AVAILABLE). The actual heat relays on at any given time
are displayed as Actual Heating Stages (ACTVE HEAT STAGE).
Heat Stage 1 Relay (HEAT 1 RELAY) and Heat Stage 2 Relay
(HEAT 2 RELAY) are displayed on when the respective relay is
energized. There are time guards to protect from short cycling, Heat
Minimum On Time (HEAT MIN ON) and Heat Minimum Off Time
(HEAT MIN OFF) apply before a heat relay can be turned back on
or turned off.
Integrated Gas Controller (IGC)
The heat staging is determined as described above and the Integrated
Gas Controller (IGC) initiates the gas heat module start- -up. The
Integrated Gas Controller (IGC) minimum on- -time of 1 minute will
be followed even if Heat Minimum On Time (HEAT MIN ON) is
lower and during Service Test. If the IGC temperature limit switch
opens within 10 minutes of the end of the gas heat cycle, the next fan
off delay will be extended by 15 seconds. The maximum delay is 3
minutes. Once modified by the IGC, the fan off delay will not change
back to the configured Fan- -off Delay, Gas Heat (HEAT FANOFF
DELAY) unless power is reset to the control. A light emitting diode
(LED) is provided on the IGC to indicate status. During normal
operation the LED is continuously on. See the Troubleshooting
section if the LED is off or flashing. The IGC is located behind the
gas section access panel door.
When the control energizes Heat Stage 1 Relay (HEAT 1 RELAY),
power is sent to the W terminal on the IGC board. A check is made to
ensure that the rollout switch and limit switch are closed. The
induced- -draft motor is then energized, and when speed is proven with
the Flue Gas Pressure switch on the motor, the ignition activation
period begins. The burners will ignite within 5 seconds. If the burners
do not light, there is a 22- -second delay before another 5- -second
attempt. If the burners still do not light, this sequence is repeated for
15 minutes. After the 15 minutes have elapsed, if the burners still have
not lit, heating is locked out. The control will reset when the request
for heat is temporarily removed. When ignition occurs the IGC board
will continue to monitor the condition of the rollout switch, limit
switches, the Flue Gas Pressure switch, as well as the flame sensor. If
the unit is controlled through a room thermostat or space sensor set for
auto- -fan, 45 seconds after ignition occurs the indoor- -fan motor will
be energized (and the outdoor- -air dampers will open to their
minimum position). If for some reason the over temperature limit
opens prior to the start of the indoor fan blower, on the next attempt,
the 45- -second delay will be shortened to 5 seconds less than the time
from initiation of heat to when the limit tripped. Gas will not be
interrupted to the burners and heating will continue. Once modified,
the fan on delay will not change back to 45 seconds unless power is
reset to the control. When the control energizes Heat Stage 2 Relay
23