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Pin #
1
Not Used
2
High Fire Pressure Switch
3
Rollout Switch In
4
Ground
5
24V Hot
6
Primary Limit In
7
Gas Valve
8
Gas Valve Common
9
24V Neutral
10
Ground
11
Primary Limit Switch Out
12
Low Fire Pressure Switch
Table 1. Control 12-Pin Terminal Designation
Pin #
1
Data Input From Motor
2
Common
3
Not Used
4
Data Output To Motor
5
5 Volt Bias Supply
6
Not Used
Table 2. Control 6-Pin Terminal Designation
Electronic Ignition
At the beginning of the heat cycle the integrated control
monitors the low fire combustion air inducer pressure switch.
The control will not begin the heating cycle if the low fire
pressure switch is closed (by-passed). Likewise the control
will not begin the high fire heating cycle if the high fire
pressure switch is closed, and will remain in low fire heat.
However, if the high fire pressure switch closes during the low
fire heat pre-purge, the control will allow high fire heat. Once
the low fire pressure switch is determined to be open, the
combustion air inducer is energized on ignition speed. When
the differential in the pressure switch is great enough, the
pressure switch closes and a 15-second pre-purge begins.
If the switch is not proven within 2-1/2 minutes, the inducer
is de-energized and the control will initiate vent calibration.
If the vent calibration is unsuccessful the control goes into
a 5 minute delay. The control will attempt vent calibration
3 more times before going into a 1 hour soft lockout. After
the 15 second pre-purge period the ignitor warms up for
20 seconds. The gas valve then opens for a 4-second trial
for ignition. The ignitor stays energized during this trial until
flame is sensed. If ignition is not proven during the 4-second
trial for ignition, the control will try four more times with an
inter purge and warm-up time between trials of 35 seconds.
After a total of five trials for ignition (including the initial trial),
the control goes into Watchguard-Flame Failure mode. After
a 60-minute reset period, the control will begin the ignition
sequence again.
Function
Function
Page 10
Thermostat Selection Modes
See Table 3 for DIP switch settings
The control can be made to operate in three modes: variable
capacity, three-stage timed or two-stage. The variable
capacity and two-stage modes are only operational with
a two-stage thermostat. The thermostat selection is made
using dip switches one and / or two (Figure 4) and must be
positioned for the particular application.
Variable Capacity
Using a two-stage thermostat the system will operate in a
variable capacity sequence mode. In this mode, the control
will vary the firing rate anywhere between 35% and 100% of
full capacity. The indoor blower will be automatically adjusted
accordingly to provide the appropriate airflow at any rate. On
the initial call for low fire, the furnace will operate at 35% and
will remain there until the heat call is satisfied or a call for
high fire is initiated. If there is a call for high fire the rate will
increase by 10% if the current rate is above 60%. However,
if the current rate is below 60% the rate will increase to 70%.
After this initial rate increase to 70% capacity, the furnace
will increase rate by 10% every 5 minutes while a high fire
heat call is present. If the high fire heat call is satisfied but
the low fire heat call is still present, the furnace will remain at
the current firing rate until the demand is satisfied or another
call for high fire is initiated.
Three-Stage Timed Operation
Using a single-stage thermostat the system will operate
in a three stage timed mode. Upon a call for heat and a
successful ignition, the combustion air inducer will operate
at 35% and the indoor blower will adjust to the appropriate
cfm. After a field selectable 7 or 12 minute delay period, the
inducer RPM will increase and the unit will operate at 70%.
The indoor blower will adjust to the appropriate cfm. After
a factory set non-adjustable 10 minute delay expires the
furnace will increase rate to 100%. The indoor blower will
adjust to the appropriate cfm.
Two-Stage Operation
The system will also operate in conventional two-stage
mode. While in two-stage mode, the furnace will fire on low
fire (70% rate). The combustion air inducer will operate at
70% and the indoor blower will adjust to the appropriate
cfm. The unit will switch to high fire on a W2 call from the
thermostat. After a 30 second recognition period (during
which the integrated control will receive a continuous W2
call) expires the furnace will increase to 100% rate. The
inducer will increase to 100% speed and the indoor blower
will adjust to appropriate cfm. If there is a simultaneous call
for first and second stage heat, the unit will fire on first stage
heat and switch to second stage heat after 30 seconds of
operation.
31-5000723 Rev. 0
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