68
The IGC boards only control the first stage of gas heat on
each gas valve. The second stages are controlled directly from
the MBB board for staged gas. For units equipped with modu-
lating gas heat, the second stage is controlled from the timer re-
lay board (TR1). The IGC board has a minimum on-time of 1
minute.
In modes such as Service Test where long minimum on
times are not enforced, the 1-minute timer on the IGC will still
be followed and the gas will remain on for a minimum of 1
minute.
Staged Gas Heat Board (SCB)
— When optional modulating
gas heat is used, the SCB board is installed and controls addi-
tional stages of gas heat. The SCB also provides additional sen-
sors for monitoring of the supply-air and limit switch tempera-
tures. For units equipped with modulating gas heat, the SCB
provides the 4 to 20 mA signal to the SC30 board that sets the
modulating gas section capacity. This board is located in the
main unit control box.
Timer Relay Control Board (TR1)
— The TR1 is used on
modulating gas heat equipped units only. It is located in the gas
heat section and is used in combination with the SC30 to pro-
vide control of the modulating gas heat section. The TR1 re-
ceives an input from the IGC, initiates a start-up sequence,
powers the SC30, sets the induced-draft motor speed, and pro-
vides the main gas valve high fire input. When the start-up se-
quence is complete, the TR1 checks the input from the SC30 to
determine which state to command the induced-draft motor
and main gas valve. See Table 45.
Signal Conditioner Control Board (SC30)
— The SC30 is
used on modulating gas heat equipped units only. It is located
in the gas heat section and is used in combination with the TR1
to provide control of the modulating gas heat section. The
SC30 is powered by an output from the TR1. It receives a
capacity input from the SCB, provides a capacity output to the
modulating gas valve, and provides an output to the TR1 to
determine which state to command the induced-draft motor
and main gas valve. See Table 45.
Modulating Gas Control Boards (SC30 and TR1) Logic
—
All gas modulating units are equipped with one timer relay
board (TR1) and one signal conditioner board (SC30), regard-
less the unit size. The boards provide control for variable heat-
ing output for the gas heat section.
Similar with staged gas heat option, each IGC board is con-
trolled separately. The IGC functions are not affected by the
modulating gas control logic. When a call for gas heat is initiat-
ed, W on the IGC board and the timer relay board (TR1) are
energized. The LED on TR1 board will be turned on. See
Table 45 for LED explanation.
When TR1 received an input from the IGC board, the relay
board starts Timer no. 1 or start-up sequence: sets the gas valve
stage and the inducer motor speed, and enables the signal con-
ditioner board SC30. During Timer no. 1, the SC30 board
keeps a fixed heating output. When Timer no. 1 expires, the
modulating gas control boards start Timer no. 2. Throughout
the duration of Timer no. 2, the boards determine which state to
adjust the capacity output to satisfy the heat demand. When
Timer no. 2 expires, the boards receive a capacity input from
the SCB board and continuous modulate the heat output until
the mode selection sensor is satisfied.
Table 44 — IGC LED Indicators
NOTES:
1. There is a 3-second pause between error code displays.
2. If more than one error code exists, all applicable error codes will
be displayed in numerical sequence.
3. Error codes on the IGC will be lost if power to the unit is
interrupted.
Table 45 — TR1 Board LED Indicators
The IGC boards only control the first stage of gas heat on
each gas valve. The second stages are controlled directly from
the MBB board. The IGC board has a minimum on-time of 1
minute.
In modes such as Service Test where long minimum on
times are not enforced, the 1-minute timer on the IGC will still
be followed and the gas will remain on for a minimum of 1
minute.
RELOCATE SAT FOR HEATING-LINKAGE APPLICA-
TIONS — If Configuration
HEAT
LAT.M is set to YES,
the supply air temperature thermistor (Temperatures
AIR.T
SAT) must be relocated downstream of the installed heating
device. This only applies to two-stage gas or electric heating
types (Configuration
HEAT
HT.CF=1 or 2).
Determine a location in the supply duct that will provide a
fairly uniform airflow. Typically this would be a minimum of
5 equivalent duct diameters downstream of the unit. Also, care
should be taken to avoid placing the thermistor within a direct
line-of-sight of the heating element to avoid radiant effects.
Run a new two-wire conductor cable from the control box
through the low voltage conduit into the space inside the build-
ing and route the cable to the new sensor location.
Installing a New Sensor
— Procure a duct-mount temperature
sensor (Carrier P/N 33ZCSENPAT or equivalent 10,000 ohm
at 25C NTC [negative temperature coefficient] sensor). Install
the sensor through the side wall of the duct and secure.
Re-Using the Factory SAT Sensor
— The factory sensor is
attached to the left-hand side of the supply fan housing.
Disconnect the sensor from the factory harness. Fabricate a
mounting method to insert the sensor through the duct wall and
secure in place.
Attach the new conductor cable to the sensor leads and ter-
minate in an appropriate junction box. Connect the opposite
end inside the unit control box at the factory leads from MBB
J8 terminals 11 and 12 (PNK) leads. Secure the unattached
PNK leads from the factory harness to ensure no accidental
contact with other terminals inside the control box.
ERROR CODE LED INDICATION
Normal Operation On
Hardware Failure Off
Fan On/Off Delay Modified 1 Flash
Limit Switch Fault 2 Flashes
Fame Sense Fault 3 Flashes
Five Consecutive Limit Switch Faults 4 Flashes
Ignition Lockout Fault 5 Flashes
Ignition Switch Fault 6 Flashes
Rollout Switch Fault 7 Flashes
Internal Control Fault 8 Flashes
Software Lockout 9 Flashes
LED
DESIGNATION
RESULT/ACTION
ON 24 VAC Supplied to TR1
SR Input received from IGC2, starts timer no. 1
MR
Modulating Gas Valve modulated except during
fixed output delay time
FR IDM2 operates at high speed
CR
Modulating Gas Valve operates in high pressure
stage
To Next Page
Loading...
