926TC: Installation, Start-up, Operating and Service and Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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7. Pour 1 quart of anti-freeze solution into the funnel/tube. Antifreeze
should run through the inducer housing, overfill condensate trap
and flow to an open drain.
8. Replace the rubber plug in the port on the collector box.
9. Remove the middle unused rubber plug from the port on the
collector box opposite the condensate trap. See Fig. 62.
10. Repeat Steps 5 through 8.
11. If a condensate pump is used, check with pump manufacturer to
verify pump is safe for use with antifreeze used. Allow pump to
start and pump anti-freeze to open drain.
12. Replace main door.
13. When furnace is re-started, flush condensate pump with clear water
to check for proper operation before re-starting furnace.
14. Propylene glycol need not be removed before re-starting furnace.
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. 61, 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 LED light will flash code 12 and display will
show (12.1) during the 90-sec 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. Perfect Heat
®
Technology - Two-Stage Heating (Adaptive
Mode) with Single-Stage Thermostat
See Fig. 39 for thermostat connections
NOTE: Heating Thermostat Type (Htt) can be set to either single stage
(1St) or two-stage (2St) on the control (see the Furnace Control
Programming and Navigation section of this instruction). When set to
(1St), the adaptive heating mode will be used in response to a call for
heat. 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 (Htt). 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, 24 VAC power is supplied for a
field installed humidifier at the HUM terminal 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 re-closes 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 energized to close
the NO 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 prepurge period after the low-heat
pressure switch LPS closes. If the high-heat pressure switch
HPS fails to close and the low-heat pressure switch LPS
closes, the furnace will operate at low-heat gas flow rate
until the high-heat pressure switch closes for a maximum of
2 minutes after ignition.
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 contact GVR closes to
energize the gas valve solenoid GV-M. The gas valve solenoid
GV-M 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. If the furnace control CPU selects high-heat
operation, the high-heat gas valve solenoid GV-HI is also
energized.
d. Flame-Proving - When the burner flame is proved at the
flame-proving sensor electrode FSE, the inducer motor IDM
switches to low-speed unless the furnace is operating in
high-heat, and the furnace control CPU begins the blower-ON
delay period and continues to hold the gas valve GV-M open. If
the burner flame is not proved within two seconds, the control
CPU will close the gas valve GV-M, 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/W1, 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 on high speed until
flame is no longer proved.
e. Blower-On delay - If the burner flame is proven the blower-ON
delays for low-heat and high-heat are as follows:
Low-heat - 45 seconds after the gas valve GV-M is opened the
blower motor BLWM is turned ON at low-heat airflow.
High-heat - 25 seconds after the gas valve GV-M is opened the
BLWM is turned ON at high-heat airflow. Simultaneously, the
electronic air cleaner terminal EAC-1 is energized and remains
energized throughout the heating cycle.
f. Switching from Low- to High-Heat - If the furnace control
CPU switches from low-heat to high-heat, the furnace control
CPU will switch the inducer motor IDM speed from low to high.
The high-heat pressure switch relay HPSR is energized to close
the NO 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 blower motor BLWM
will transition to high-heat airflow five seconds after the furnace
control CPU switches from low-heat to high-heat.
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