PG80MSU: 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.
34
A190291
Fig. 39 – Cleaning Heat Exchanger Cell
SEQUENCE OF OPERATION
NOTE:
Furnace control must be grounded for proper operation of
furnace control and flame sensing electrode. Control is grounded
through green/yellow wire routed to gas valve and burner box screw.
Using the schematic diagram in
, 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 2 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-second period, after which the LED will be ON continuous, as long
as no faults are detected. After the 90-second blower-ON 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.
Call for Heat:
The wall thermostat “calls for heat”, closing the R
-
W circuit. The
furnace control performs a self-check, verifies the transducer reads
no pressure present, and starts the inducer motor IDM ramp to
prepurge
a.
Inducer Prepurge Period:
The furnace control CPU ramps up
the inducer motor IDM to prepurge pressure then the furnace
control CPU begins a 15-second prepurge period. If the
transducer fails to reach target pressure the inducer motor IDM
will remain running until target pressure is maintained.
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. Inducer maintains pressure during igniter
warm-up. If inducer prepurge and igniter warm up sequence is
not completed in 5 minutes, the unit will shut down and LED
light will flash code 31. Retry occurs after 2 minutes.
c.
Trial for Ignition:
When the igniter warm-up period is
completed the main gas valve relay contact GVR closes to
energize the gas valve solenoid GV. The gas valve solenoid 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
sensor electrode FSE, the inducer motor IDM will increase speed
(after a short delay of 14 seconds on some modes) to a higher
RUN pressure. The control will maintain this pressure once
reached, and the furnace control CPU will begin the blower-ON
delay period while continuing to hold the gas valve GV open. If
the burner flame is not proved within the 2-second flame proving
period, the control CPU will open the gas valve relay GVR,
de-energizing the gas valve solenoid GV. The control CPU will
repeat the ignition sequence for up to three more
Trials-for-Ignition before going to an Ignition-Lockout. Lockout
will be reset automatically after 3 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 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 turned on at HEAT speed 25 seconds after the gas valve
GV is energized.
Simultaneously, the humidifier terminal HUM and electronic air
cleaner terminal EAC-1 are energized and remain energized
throughout the heating cycle.
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 15-second post-purge period. The blower motor BLWM and
air cleaner terminal EAC-1 will remain ON at heat airflow 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.
2. The thermostat “calls for cooling”.
a.
Single-Speed Cooling
-
The thermostat closes the R-to-G-and-Y circuits. The R-to-Y
circuit starts the outdoor unit, and the R-to-G-and-Y/Y2 circuits
start the furnace blower motor BLWM on COOL speed. The
electronic air cleaner terminal EAC-1 is energized with 115 VAC
when the blower motor BLWM is operating.
When the thermostat is satisfied, the R-to-G-and-Y/Y2 circuits
are opened. The outdoor unit will stop, and the furnace blower
motor BLWM will continue operating on the COOL speed for an
additional 5, 30, or 90 seconds (depending on the cooling
blower-OFF delay selection). The furnace CPU is factory set for
a 90 second cooling blower-OFF delay. (See
).
b. Two-Stage Thermostat and Two-Speed Cooling
The thermostat closes the R-to-G-and-Y1 circuits for
low-cooling or closes the R-to-G-and-Y1-and-Y/Y2 circuits for
high-cooling. The R-to-Y1 circuit starts the outdoor unit on
low-cooling speed, and the R-to-G-and-Y1 circuit starts the
furnace blower motor BLWM at low-cooling airflow. The
R-to-Y1-and-YY/2 circuits start the outdoor unit on high-cooling
speed, and the R-to-G-and-Y/Y2 circuits start the furnace blower
motor BLWM at high-cooling airflow. Terminal EAC-1 is
energized with as long as the blower motor BLWM is ON.
When the thermostat is satisfied, the R-to-G-and-Y1 or R-to-
G-and-Y1-and-Y2 circuits are opened. The outdoor unit stops,
and the furnace blower BLWM and electronic air cleaner
terminal EAC-1 will remain energized for an additional
90-seconds.
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.
