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-oz. 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 switch(es).
d.Limit over-temperature switch.
e.Gas valve.
f.Hot surface igniter.
g.Flame-sensing electrode.
h.Flame rollout switches.
i.Install NOx baffles (if removed).
14.Reinstall internal vent pipe, if applicable.
A91252
Fig. 58 - Cleaning Heat Exchanger Cell
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.
19.Check for gas leaks.
20.Replace outer access door.
!WARNING
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal injury, death and/or property damage.
Never purge a gas line into a combustion chamber. Never test for gas leaks with an open flame. Use a commercially available soap solution made specifically for the detection of leaks to check all connections.
Sequence of Operation
NOTE: Furnace control must be grounded for proper operation or control will lock out. Control is grounded through green/yellow wire routed to gas valve and manifold bracket 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), 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.Heating
(See Fig. 25 for thermostat connections.)
The wall thermostat “calls for heat,” closing the R-to-W circuit. The furnace control performs a self-check, verifies the pressure switch contacts PRS are open, and starts the inducer motor IDM.
a.Inducer Prepurge Period- As the inducer motor IDM comes up to speed, the pressure switch contacts PRS close to begin a 15-second prepurge period.
b.Igniter Warm-Up- At the end of the prepurge period, the Hot-Surface igniter HSI is energized for a 17-second igniter warm-up period.
c.Trial-for-Ignition Sequence- When the igniter warm-up period is completed, the main gas valve relay contacts GVR close to energize the gas valve GV, the gas valve opens, and 24 vac power is supplied for a field-installed humidifier at the HUM terminal. The gas valve GV permits gas flow to the burners where it is ignited by the HSI. Five seconds after the GVR closes, a 2-second flame proving period begins. The HSI igniter will remain energized until the flame is sensed or until the 2-second flame proving period begins.
d.Flame-Proving- When the burner flame is proved at the flame-proving sensor electrode FSE, the furnace control CPU begins the blower-ON delay period and continues to hold the gas valve GV open. If the burner flame is not proved within two seconds, the control CPU will close the gas valve GV, and the control CPU will repeat the ignition sequence for up to three more Trials-For-Ignition before going to Ignition-Lockout. Lockout will be reset automatically after three hours or by momentarily interrupting 115 vac power to the furnace, or by interrupting 24 vac power at SEC1 or SEC2 to the furnace control CPU (not at W, G, R, etc.). If flame is proved when flame should not be present, the furnace control CPU will lock out of Gas-Heating mode and operate the inducer motor IDM until flame is no longer proved.
e.Blower-On Delay- If the burner flame is proven, the blower motor is energized on HEAT speed 25 seconds after the gas valve GV is energized.
Simultaneously, the electronic air cleaner terminal EAC-1 is energized and remains energized as long as the blower motor BLWM is energized.
f.Blower-Off Delay- When the thermostat is satisfied, the R-to-W circuit is opened, de-energizing the gas valve GV, stopping gas flow to the burners, and de-energizing the humidifier terminal HUM. The inducer motor IDM will remain energized for a 5-second post-purge period. The blower motor BLWM and air cleaner terminal EAC-1 will remain energized for 90, 120, 150, or 180 seconds (depending on the blower-OFF delay selection). The furnace control CPU is factory-set for a 120-second blower-OFF delay.
