Bryant GAMA 331JAV - Manual (Page 10)

The gas service pressure must not exceed 0.5 psig (14-in. wc), and
be no less than 0.16 psig (4.5-in. wc).
Thermostat wire connections at R and W/W1 are the minimum
required for gas heating operation. W2 must be connected for
2-stage heating thermostats. C
OM
, Y/Y2, and G are required for
cooling, heat pumps, and some clock thermostats. These must be
made at 24-v terminal block on control. (See Fig. 10.)
This furnace can be installed with either single-stage heating or
2-stage heating thermostat.
For single-stage thermostats, connect thermostat W to W/W1 at
furnace control terminal block. (See Fig. 11.) For single-stage
thermostats the control determines, based on length of previous
heating on and off cycles, when to operate in low- and high-gas
heat for optimum comfort. Setup Switch-2 (SW-2) must be in the
factory-shipped OFF position. See Fig. 13 and Tables 6 and 7 for
setup switch information.
If 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 stage and allows 2-stage
thermostat to select gas heating modes. The W2 from thermostat
must be connected to W2 on control terminal block. (See Fig. 12.)
Before operating furnace, check each manual reset switch for
continuity. If necessary, press and release button to reset switch.
CAUTION: This furnace is equipped with 2 manual
reset limit switches in gas control area. The switches will
open and shut off power to gas valve if a flame rollout or
an overheating condition occurs in gas control area. DO
NOT bypass switches. Correct inadequate combustion air
supply, component failure, restricted flue gas passageway
before resetting switches.
B. Sequence of Operation
Using the schematic diagram follow sequence of operation through
different modes. (See Fig. 14.) Read and follow wiring diagram
very carefully.
NOTE: If power interruption occurs during "call for heat" (W/W1
or W/W1-and-W2), control starts 90-sec blower only on period 2
sec after power is restored if thermostat is still calling for gas
heating. The red LED flashes code 12 during 90-sec period, after
which LED will be on continuously as long as no faults are
detected. After 90-sec period, furnace responds to thermostat
normally.
Blower door must be installed for power to be conducted through
blower door interlock switch ILK to furnace control CPU, trans-
former TRAN, inducer motor IDM, blower motor BLWM, hot
surface ignitor HSI, and gas valve GV.
1. Adaptive Heating Mode—Single-Stage Thermostat and
2-Stage Heating
(See Fig. 11 for thermostat connections.)
NOTE: With high-heat-only switch SW-1 off, low-heat-only
switch SW-2 selects either low-heat-only operation mode when on
(see item 2 below), or adaptive heating mode when off in response
to "call for heat." (See Fig. 13.) When high-heat-only switch SW-1
is on, it always causes high-gas-heat operation when R-W/W1
circuit is closed, regardless of the 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 in-
cludes a programmed adaptive sequence of controlled
operation which selects low-gas-heat or high-gas-heat op-
eration. This selection is based upon stored history of the
length of previous gas heating on/off periods of single-stage
thermostat.
The furnace starts up in either low- or high-gas heat. If
furnace starts up in low-gas heat, control CPU determines
low-gas heat on time (from 0 to 16 minutes) which is
permitted before switching to high-gas heat.
If power is interrupted, stored history is erased, and control
CPU selects low-gas heat for up to 16 minutes and then
switches to high-gas heat as long as thermostat continues to
"call for heat." Subsequent selection is based on stored
history of thermostat cycle times.
When the wall thermostat "calls for heat," R-W1 circuit
closes. The furnace control performs a self-check, verifies
low-heat and high-heat pressure switch contacts LPS and
HPS are open, and starts inducer motor IDM in low speed
or high speed as appropriate.
TABLE 6—SETUP SWITCH DESCRIPTION
SETUP
SWITCH NO.
NORMAL
POSITION
DESCRIPTION OF USE
SW-1
Only High-Gas Heat
OFF
(Staged Gas
Heat)
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.
SW-2
Low-Gas Heat
(Adaptive Mode)
OFF
(Single-Stage
Thermostat)
Turn switch off for installations
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 op-
eration in response to closing
R-W/W1. High-gas heat is
supplied only when R to
W/W1 and W2 is closed.
SW-3 and
SW4
ON, OFF
Switches control gas heating
blower off delay. (See Table
7.)
TABLE 7—BLOWER OFF DELAY
SETUP SWITCH POSITION
DESIRED HEATING
MODE BLOWER OFF
DELAY (SEC)
SETUP SWITCH
SW-3 SW-4
90 OFF OFF
135 OFF ON
180 ON OFF
225 ON ON
→ Fig. 13—Setup Switches on Control Center
(Factory Settings)
A96402
BLOWER-
OFF
DELAY
LOW
HEAT
(ADAPTIVE
ALGORITHM)
HIGH
HEAT
ONLY
4 3 2
OFF
ON
1
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