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Table 55 — SCR Electric Heat
NUMBER
HT.ST
UNIT SIZE
OF
CONFIG
STAGES
6
030-070
1
6
030-070
7
030-050
2
8
055-070
Table 56 — SCR Electric Heat Control Steps
(HT.ST=6)
RELAY OUTPUT
STAGE
Heat1
0
OFF
1
ON
Table 57 — SCR Electric Heat Control Steps
(HT.ST=7)
RELAY OUTPUT
STAGE
Heat1
0
OFF
1
ON
2
ON
Table 58 — SCR Electric Heat Control Steps
(HT.ST=8)
RELAY OUTPUT
STAGE
Heat1
0
OFF
1
ON
2
ON
Limit Switch Temperature Monitoring (LIM.M)
Variable air volume applications in the low heat or tempering
mode can experience low airflow and as a result it is possible for
nuisance trips of the gas heat limit switch, thereby shutting off
all gas stages. In order to achieve consistent heating in a temper-
ing mode, a thermistor (Temperatures
placed next to the limit switch and monitored for overheating. In
order to control a tempering application where the limit switch
temperature has risen above either the upper or lower configura-
tion parameters (SW.L.T, SW.H.T), the staged gas control will
respond by clamping or dropping gas stages.
If the Limit Switch Monitoring configuration parameter (LIM.M)
is set to YES, all the modes will be monitored. If set to NO, then
only LAT Cutoff mode and Capacity Clamp mode for RISE will
be monitored.
If S.G.LS rises above SW.L.T or if (LAT – LAT last time through
the capacity calculation) is greater than (RISE) degrees F per sec-
ond, the control will not allow the capacity routine to add stages
and will turn on the Capacity Clamp mode.
If S.G.LS rises above SW.H.T, the control will run the capacity
routine immediately and drop all heat stages and will turn on the
Limiting mode.
If S.G.LS falls below SW.L.T, the control will turn off both Capac-
ity Clamp mode and Limiting mode with one exception. If (LAT –
LAT last time through the capacity calculation) is greater than
"RISE" degrees F per second, the control will stay in the Capacity
Clamp mode.
If control is in the Limiting mode and then S.G.LS falls below
SW.L.T, and LAT is not rising quickly, the control will run the
capacity calculation routine immediately and allow a full stage
to come back on if desired this first time through upon recovery.
This will effectively override the "max capacity stage" clamp.
In addition to the above checks, it is also possible at low cfm for
the supply-air temperature to rise and fall radically between ca-
pacity calculations, thereby impacting the limit switch tempera-
ture. In the case where supply-air temperature (LAT) rises above
HEAT
VOLTAGE
50P
SIZE
Low, Medium
208/230
All
380,460,575
High
208/230
High
208/230
CAPACITY (%)
Heat2
Min.
Max.
OFF
0
0
ON
0
100
CAPACITY (%)
Heat2
Min.
Max.
OFF
0
0
OFF
0
67
ON
0
100
CAPACITY (%)
Heat2
Min.
Max.
OFF
0
0
OFF
0
50
ON
50
100
AIR.T
S.G.LS) is
the control point (HT.C.P) + the cutoff point (LAT.L) the control
will run the capacity calculation routine immediately and drop a
stage of heat. Thereafter, every time the capacity calculation rou-
tine runs, provided the control is still in the LAT cutoff mode
condition, a stage will drop each time through. Falling back be-
low the cutoff point will turn off the LAT cutoff mode.
CONTROL BOARD INFORMATION
Integrated Gas Control (IGC)
One IGC is provided with each bank of gas heat exchangers. Low
heat size 030-050 units use one IGC; high heat size 030-050 units
and low heat 055-100 units use two; and high heat 055-100 units
use three. The IGC controls the direct spark ignition system and
monitors the rollout switch, limit switches, and induced-draft mo-
tor Hall Effect switch. For units equipped with modulating gas
heat, the IGC in the modulating gas section uses a pressure switch
in place of the Hall Effect sensor. The IGC is equipped with a
LED (light-emitting diode) for diagnostics. See Table 59.
Table 59 — IGC LED Indicators
ERROR CODE
Normal Operation
Hardware Failure
Fan On/Off Delay Modified
Limit Switch Fault
Fame Sense Fault
Five Consecutive Limit Switch Faults
Ignition Lockout Fault
Ignition Switch Fault
Rollout Switch Fault
Internal Control Fault
Software Lockout
NOTE(S):
a. There is a 3-second pause between error code displays.
b. If more than one error code exists, all applicable error codes will be displayed
in numerical sequence.
c. Error codes on the IGC will be lost if power to the unit is interrupted.
Integrated Gas Control Board Logic
This board provides control for the ignition system for the gas heat
sections.
When a call for gas heat is initiated, power is sent to W on the IGC
boards. For standard 2-stage heat, all boards are wired in parallel.
For staged gas heat, each board is controlled separately. When en-
ergized, an LED on the IGC board will be turned on. See Table 59
for LED explanations.
Each board will ensure that the rollout switch and limit switch are
closed. The induced-draft motor is then energized. For units
equipped with 2-stage or staged gas heat, the speed of the motor is
proven with a Hall Effect sensor on the motor. For units equipped
with modulating gas heat, the motor function is proven with a
pressure switch. When the motor speed or function is proven, the
ignition activation period begins. The burners ignite within 5 sec-
onds. If the burners do not light, there is a 22 second delay before
another 5 second attempt is made. If the burners still do not light,
this sequence is repeated for 15 minutes. After 15 minutes have
elapsed and the burners have not ignited, then heating is locked
out. The control will reset when the request for W (heat) is tempo-
rarily removed.
When ignition occurs, the IGC board will continue to monitor the
condition of the rollout switch, limit switches, Hall Effect sensor
or pressure switch, and the flame sensor. Forty-five seconds after
ignition has occurred, the IGC will request that the indoor fan be
turned on.
The IGC fan output (IFO) is connected to the indoor fan input on
the MBB which will indicate to the controls that the indoor fan
should be turned on (if not already on). If for some reason the
overtemperature limit switch trips prior to the start of the indoor
fan blower, on the next attempt the 45 second delay will be short-
ened by 5 seconds. Gas will not be interrupted to the burners and
70
a,b,c
LED INDICATION
On
Off
1 Flash
2 Flashes
3 Flashes
4 Flashes
5 Flashes
6 Flashes
7 Flashes
8 Flashes
9 Flashes
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Troubleshooting
