Carrier WEATHERMAKER 48A4, Wiring Diagrams

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If the control is connected to a ComfortID™ system, the
room terminals are equipped with microprocessor controls that
give commands to the base module. If linkage is active, the
control module will replace local Comfort Link™ set points
and occupancy data with linkage supplied data.
If Temperature Compensated Start is active, then the unit
control will start the unit in advance of the occupied time to
pre-cool or heat the space. If the unit is configured to use a
pre-purge cycle, then the control will start the unit in vent mode
based on a pre-start time interval. If an IAQ (indoor air quality)
sensor is being used and the low IAQ control point is satisfied
then the mode will be terminated. The mode terminates when
the occupied period starts.
If Cooling mode is required, then the controlling set point
will be the leaving evaporator air temperature set point. If an
economizer is present and the changeover control allows the
economizer to be used, then the control will first attempt to
control the leaving evaporator air temperature using free
cooling. If this cannot satisfy the load then additional
compressor stages will be turned on to maintain the leaving air
temperature. When both compressors and the economizer are
being used, the unit control will use the economizer dampers to
maintain better control of the leaving air and to prevent high
compressor cycling. If the economizer cannot be used, then it
will be set to the minimum vent position.
If the unit is equipped with an optional hot gas bypass valve,
then the unit control will use hot gas as an additional stage of
capacity. When the first stage of cooling is required, the unit
control will turn on the circuit A compressor and the hot gas
bypass valve. When additional cooling is called for, the unit
control will turn off the hot gas bypass valve. The valve will
also be used for additional freeze protection of the coils when
low evaporator refrigerant temperatures are detected using the
suction pressure tranducers.
The unit control will also monitor the supply duct pressure
and send a 4 to 20 mA signal to the factory-supplied inverter to
control the speed of the fan to maintain the user-configured
supply duct status pressure. If the Comfort Link control is on
the CCN (Carrier Comfort Network ® ) system or a building
linkage system, then the control also supports static pressure
reset based on the needs of the zones.
If the unit has been enabled for occupied heat and if the
space temperature sensor (SPT), return air temperature sensor
(RAT), or CCN (in a building linkage system) demand requires
that the unit be in Heating mode, then the unit control will
energize the electric or gas heat to warm the space. In this
mode, the unit control will energize the heat interlock relay
(HIR). Note that for the linkage systems the interlock relay
connection is not required. Once the mode is enabled, the unit
control will use up to 2 stages of heat to control to the return air
temperature set point. Heating will continue until the return
temperature set point is satisfied. If the unit is configured for
morning warm-up and the heating demand is below the set
point during the first 10 minutes of operation, then the unit
control will energize full heating capacity until the return air
temperature set point is satisfied.
Gas Heat Unit Operation —
The gas heat units incor-
porate 2 (3 on size 060) separate systems to provide gas heat.
Each system incorporates its own induced-draft motor,
Integrated Gas Control (IGC) board, 2-stage gas valve,
manifold, and safeties. The systems are operated in parallel.
For example, when there is a call for first stage heat, both
induced-draft motors operate, both gas valves are energized,
and both IGC boards initiate spark. All of the gas heating
control is performed through the IGC boards (located in the
heating section).
The MBB (Main Base Board) module board initiates and
terminates heating operation and monitors the status of the
requirements for indoor fan operation. The fan will be
controlled directly by the MBB board.
When the thermostat or room sensor calls for heating, the
MBB board will close heating relays and send power to W on
each of the IGC boards. An LED on the IGC board will be on
during normal operation. A check is made to ensure that the
rollout switches and limit switches are closed and the induced-
draft motors are not running. After the induced-draft motors are
energized and speed is proven with the Hall Effect sensor on
the motor, the ignition activation period begins. The burners
will ignite within 5 seconds. When ignition occurs the IGC
board will continue to monitor the condition of the rollout and
limit switches, the Hall Effect sensor and the flame sensor.
If the unit is controlled through a room thermostat set for
fan auto., 45 seconds after ignition occurs the indoor-fan motor
will be energized and the outdoor-air dampers will open to their
minimum position. If the overtemperature 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.
If the unit is controlled through a room sensor, the indoor
fan will operate in the occupied mode and the outdoor-air
dampers will be at the minimum position. In the unoccupied
mode, the indoor fan will be energized through the IGC board
with a 45-second delay and the outside-air dampers will move
to the minimum unoccupied set point.
When additional heat is required, the second stage MBB
output relay closes and initiates power to the second stage of all
main gas valves in all sections. When the demand is satisfied,
MBB heat output relays will open and the gas valves close
interrupting the flow of gas to the main burners.
If the call for stage 1 heat lasts less than 1 minute, the
heating cycle will not terminate until 1 minute after W1
became active. If the unit is configured for intermittent fan then
the indoor-fan motor will continue to operate for an additional
45 seconds then stop and the outdoor-air dampers will close. If
the over temperature limit opens after the indoor motor is
stopped within 10 minutes of W1 becoming inactive, on the
next cycle the time will be extended by 15 seconds. The
maximum delay is 3 minutes. Once modified, the fan off delay
will not change back to 45 seconds unless power is reset to the
control.
Indoor Air Quality —
The indoor air quality (IAQ) func-
tion provides a demand-based control for ventilation air quanti-
ty, by providing a modulating outside air damper position that
is proportional to space CO
2
level. The ventilation damper po-
sition is varied between a minimum ventilation level (based on
internal sources of contaminants and CO
2
levels other than the
effect of people) and the maximum design ventilation level
(determined at maximum populated status in the building).
During a less-than-fully populated space period, the CO
2
level
will be lower than maximum design ventilation level at full-
load design condition, thus less ventilation air will be required.
Reduced quantities of ventilation air will result in reduced op-
erating costs. Space CO
2
level is monitored and compared to
user-configured set points. An accessory CO
2
sensor for space
(or return duct mounting) is required. The IAQ routine can be
enhanced by also installing a sensor for outdoor air quality
(OAQ).