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SETUP
SWITCH NO.
SW-1
Only High-Gas Heat
SW-2
Low-Gas Heat (Adaptive Mode)
SW-3 and SW-4
4
3
BLOWER-
OFF
DELAY
Fig. 50—Setup Switches on Control Center
(Factory Settings)
TABLE 10—BLOWER OFF DELAY SETUP SWITCH (SW)
POSITION
DESIRED HEATING
MODE BLOWER-OFF
DELAY (SEC)
90
135
180
225
If a 2-stage heating thermostat is to be used, move SW-2 to ON
position at end of furnace installation. This overrides built-in
control process for selecting high and low fire and allows the
2-stage thermostat to select gas heating modes. The W2 from
thermostat must be connected to W2 on control terminal block.
(See Fig. 28.)
Before operating furnace, check each manual reset switch for
continuity. If necessary, press and release button to reset switch.
The blower compartment door must be in place to complete the
115-v circuit to the furnace.
TABLE 9—SETUP SWITCH DESCRIPTION
NORMAL
POSITION
OFF (Staged Gas Heat)
OFF (Single-Stage Thermostat)
ON, OFF
2
1
OFF
ON
LOW
HIGH
HEAT
HEAT
(ADAPTIVE
ONLY
ALGORITHM)
A96402
SETUP SWITCH
SW-3
SW-4
OFF
OFF
OFF
ON
ON
OFF
ON
ON
Turn switch on to obtain only high-gas heat operation, on
any call for heat regardless of whether R-W/W1, or
R-W/W1, -W2 is closed. SW-1 overrides SW-2.
Turn switch off for installation with single-stage thermostats;
control selects low-gas-heat or high-gas-heat operation
based on previous cycles. Turn switch on for installations
with 2–stage thermostats to permit only low-gas-heat opera-
tion in response to closing R-W/W1. High-gas heat is sup-
plied only when R to W/W1 and W2 are closed.
Switches control gas heating mode blower off delay. (See
CAUTION: This furnace is equipped with a manual
reset limit switch in the gas control area. The switch will
open and shut off power to the gas valve if a flame rollout
or overheating condition occurs in the gas control area.
DO NOT bypass the switch. Correct inadequate
combustion-air supply, component failure, or restricted
flue gas passageway before resetting the switch.
II. SEQUENCE OF OPERATION
Using schematic diagram in Fig. 31, follow the sequence of
operation through the different modes. Read and follow diagram
very carefully.
NOTE: If power interruption occurs during "call for heat" (W/W1
or W/W1 and W2), the control will start a 90-sec blower-only ON
period 2-sec after power is restored, and if the thermostat is still
calling for gas heating. The red LED will flash code 12 during the
90-sec period, after which the LED will be on continuous as long
as no faults are detected. After the 90-sec period, the furnace will
respond to the thermostat normally.
The blower door must be installed for power to be conducted
through blower door interlock switch ILK to furnace control CPU,
transformer TRAN, inducer motor IDM, blower motor BLWM,
hot surface ignitor HSI, and gas valve GV.
A. Two-Stage Heating With Single-Stage Thermostat
(Adaptive Mode)
(See Fig. 27 for thermostat connections.)
NOTE: With high-heat-only switch SW-1 off, low-heat-only
switch SW-2 selects either the low-heat-only operation mode when
on (see item 2 below), or adaptive heating mode when off in
response to a call for heat. (See Fig. 32.) When high-heat-only
switch (SW-1) is in ON position, it always causes high-gas-heat
operation when R-W/W1 circuit is closed, regardless of setting of
low-heat-only switch (SW-2).
This furnace can operate as a 2-stage furnace with a single-stage
thermostat because furnace control CPU includes a programmed
adaptive sequence of controlled operation, which selects low-gas-
heat or high-gas-heat operation. This selection is based upon the
stored history of the length of previous gas heating on/off periods
of the single-stage thermostat.
The furnace will start up in either low- or high-gas heat. If the
furnace starts up in low-gas heat, the control CPU determines the
low-gas heat on time (from 0 to 16 minutes) which is permitted
before switching to high-gas heat.
If power is interrupted, the stored history is erased. When this
happens, the control CPU will initially select low-gas heat for up
to 16 minutes and then switch to high-gas heat, as long as the
thermostat continues to call for heat. Subsequent selection is based
on stored history of thermostat cycle times.
—33—
DESCRIPTION
OF USE
Table 9)
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