43
If the indoor fan control is configured to cycle with the heat-
ing demand (
Configuration
→
UNIT
→
OC.FN =
No
) the
fan will stop after a configured delay,
Configuration
→
HEAT
→
FOD.G
. Factory default value is 45 seconds. If the
IGC temperature limit switch opens within 10 minutes of the
end of the gas heating, the next fan off delay will be extended
by 15 seconds. The maximum delay is 3 minutes. Once modi-
fied by the IGC, the fan off delay will not change back to
FOD.G
unless power is reset to the control.
A light-emitting-diode (LED) is provided on the IGC
(integrated gas controller) to indicate its 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
gas section access panel. See Fig. 5 for location.
THERMOSTAT CONTROL — When the thermostat calls
for heating, the MBB senses that W1 is On and closes the HT.1
relay. When the relay is closed, it sends power to W on the IGC
(integrated gas unit controller) board. An LED (light-emitting
diode) on the IGC board will be on during normal operation.
A check is made to ensure that the rollout switch and limit
switch are closed. The induced-draft motor is then energized.
When speed is proven with the Hall Effect sensor 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 ignited, 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 moni-
tor the condition of the rollout switch, limit switches, 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
for some reason 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.
When additional heat is required and the MBB senses that
W2 is On, the MBB will turn on the HT.2 relay which sends
power to the second stage of the main gas valve. If the thermo-
stat removes the call for W2, the unit will turn off HT.2. If W1
is satisfied, the MBB will turn off HT.1 which will turn off gas
to the main burners.
If the user has selected Adaptive (see Cooling section) for
its thermostat mode, the algorithm will follow the configurable
delays for adding and removing stages. When adding addition-
al heat stages, the delay is measured from when the last stage
was added (
Configuration
→
HEAT
→
H.INC
). When remov-
ing stages, the delay is measured from when the last stage was
removed (
Configuration
→
HEAT
→
H.DEC
). Therefore, if
W1 and W2 turn on simultaneously, the second stage will turn
on after a
H.INC
delay.
NOTE: If the mode is not Adaptive, then there are no delays
for adding and removing stages.
SPACE SENSOR CONTROL — To operate the unit in
Space Sensor mode, set the Unit Control Type to 3 (
Configura-
tion
→
UNIT
→
U.CTL
=3). To enable heating during space
temperature control, a jumper wire must be added between R
and W1 on the field connection terminal strip (see Major
System Components section for wiring diagrams).
Because Space Sensor mode is an “Auto” mode, the control
will switch between cooling and heating to maintain space
temperature. However, to minimize unnecessary changes, there
is a 10-minute mode select timeguard (
Operating Modes
→
HEAT
→
MS.TG
) after the last stage of cool turns off before
heating is allowed.
The unit tries to maintain the space temperature at the Occu-
pied Heat Set Point (
Setpoints
→
OHSP
) or the Unoccupied
Heat Set Point (
Setpoints
→
UHSP
). See the Occupancy Deter-
mination section for factors that affect the Occupied status
(
Run Status
→
VIEW
→
OCC
). Heating Demand (
Operating
Modes
→
HEAT
→
SPT
→
DMD.H
) is equal to the occupied or
unoccupied set point minus the Space Temperature (
Operating
Modes
→
HEAT
→
SPT
→
SPT
).
DMD.H
= setpoint –
SPT
Two methods are used to add and remove stages of heating
for units with more than one heat stage. The first method caus-
es the unit to operate around its steady-state number of stages.
For example, if the correct number of stages is between 0
and 1, this method will cause the first stage to cycle. If the cor-
rect number of stages is between 1 and 2, this method will
cause the second stage to cycle. The second method causes the
unit to find the steady-state number of stages. Details of these
methods are provided below.
CONTROL BOX
FILTER ACCESS
DOOR
GAS SECTION
OUTDOOR AIR
SCREEN
(HIDDEN)
PEM 1 & 2
CO SENSOR
2
RETURN SMOKE
DETECTOR
SMOKE CONTROL
MODULE
CONVENIENCE
OUTLET
Fig. 5 — Panel and Filter Locations (48PG Unit Shown)
a48-7777
Summary of Contents for 48PG24
Page 68: ...68 Fig 14 Low Voltage Control Schematic 48PG20 28 Units without Humidi MiZer System a48 7627...
Page 69: ...69 Fig 15 Low Voltage Control Schematic 48PG20 28 Units with Humidi MiZer System a48 8227...
Page 70: ...70 Fig 16 Low Voltage Control Schematic 50PG20 28 Units without Humidi MiZer System a48 7778...
Page 71: ...71 Fig 17 Low Voltage Control Schematic 50PG20 28 Units with Humidi MiZer System a50 8101...
Page 72: ...72 Fig 18 Power Schematic Units without Humidi MiZer System a48 7628...
Page 73: ...73 Fig 19 Power Schematic Units with Humidi MiZer System a48 8228...
Page 74: ...74 Fig 20 Component Arrangement Units without Humidi MiZer System a48 8229...
Page 75: ...75 Fig 21 Component Arrangement Units with Humidi MiZer System a48 8230...
Page 105: ......