55
A releasing agent such as cooking spray or equivalent
(must not contain corn or canola oil, aromatic or
halogenated hydrocarbons or inadequate seal may occur)
and RTV sealant (G.E. 162, 6702, or Dow-- Corning 738)
are needed before starting installation. DO NOT substitute
any other type of RTV sealant. G.E. 162 (P771--9003) is
available through RCD in 3--o z tubes.
12. Apply new sealant to flange of collector box and attach to
cell panel using existing screws, making sure all screws
are secure.
13. Reconnect wires to the following components (Use
connection diagram on wiring label, if wires were not
marked for reconnection locations.):
a. Draft safeguard switch.
b. Inducer motor.
c. Pressure switches.
d. Limit overtemperature switch.
e. Gas valve.
f. Hot surface igniter .
g. Flame--sensing electrode.
h. Flame rollout switches.
14. Reinstall internal vent pipe, if applicable.
15. Reinstall vent connector on furnace vent elbow. Securely
fasten vent connector to vent elbow with 2 field--supplied,
corrosion--resistant, sheet metal screws located 180_ apart.
16. Replace blower access door only if it was removed.
17. Set thermostat above room temperature and check furnace
for proper operation.
18. Verify blower airflow and speed changes between heating
and cooling.
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage. Never use a match or
other open flame to check for gas leaks. Use a
soap--and--water solution.
!
WARNING
19. Check for gas leaks.
Sequence of
Operation
NOTE: Furnace control must be grounded for proper operation
or else control will lock out. Control is grounded through
green/yellow wire routed to gas valve and burner box screw.
Using the schematic diagram in Fig. 59, follow the sequence of
operation through the different modes. Read and follow the
wiring diagram very carefully .
NOTE: If a power interruption occurs during a call for heat
(W/W1 or W/W1 -- and--W2), the control will start a 90--second
blower-- only ON period two seconds after power is restored, if
the thermostat is still calling for gas heating. The amber LED
light will flash code 12 during the 90--second period, after which
the LED will be ON continuous, as long as no faults are detected.
After the 90--second period, the furnace will respond to the
thermostat normally .
The blower door must be installed for power to be conducted
through the blower door interlock switch ILK to the furnace
control CPU, transformer TRAN, inducer motor IDM, blower
motor BLWM, hot --surface igniter HSI, and gas valve GV.
1. Two--Stage Heating (Adaptive Mode) with Single--Stage
Thermostat
See Fig. 28 -- 35 for thermostat connections
NOTE: The low--heat only switch SW1--2 selects either the
low-- heat only operation mode when ON, (see item 2. below) or
the adaptive heating mode when OFF in response to a call for
heat. (See Table 8.) When the W2 thermostat terminal is
energized it will always cause high-- heat operation when the
R--to--W circuit is closed, regardless of the setting of the low--heat
only switch. This furnace can operate as a two--stage furnace with
a single--stage thermostat because the furnace control CPU
includes a programmed adaptive sequence of controlled
operation, which selects low-- heat or high --heat operation. This
selection is based upon the stored history of the length of
previous gas-- heating periods of the single-- stage thermostat.
The furnace will start up in either low-- or high--heat. If the
furnace starts up in low--heat, the control CPU determines the
low--heat on--time (from 0 to 16 minutes) which is permitted
before switching to high--heat.
If the power is interrupted, the stored history is erased and the
control CPU will select low--heat for up to 16 minutes and then
switch to high --heat, as long as the thermostat continues to call for
heat. Subsequent selection is based on stored history of the
thermostat cycle times.
The wall thermostat “calls for heat”, closing the R--to--W circuit.
The furnace control performs a self--check, verifies the low--heat
and high--heat pressure switch contacts LPS and HPS are open,
and starts the inducer motor IDM in high--speed.
a. Inducer Prepurge Period
(1.) If the furnace control CPU selects low--heat
operation the inducer motor IDM comes up to
speed, the low--heat pressure switch LPS closes,
and the furnace control CPU begins a 15-- second
prepurge period. If the low--heat pressure switch
LPS fails to remain closed the inducer motor
IDM will remain running at high-- speed. After the
low--heat pressure switch recloses the furnace
control CPU will begin a 15--second prepurge
period, and continue to run the inducer motor
IDM at high--speed.
(2.) If the furnace control CPU selects high--heat
operation, the inducer motor IDM remains
running at high --speed, and the high --heat
pressure switch relay HPSR is de--energized to
close the NC contact. When sufficient pressure is
available the high-- heat pressure switch HPS
closes, and the high-- heat gas valve solenoid
GV--HI is energized. The furnace control CPU
begins a 15--second
315A
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