78
440 01 4800 01
Specifications subject to change without notice.
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. 72, 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 1+2 during the 90--second period, after which the
LED will be flashing a heartbeat (bright--dim), 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. 39 and 40 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 Fig. 64. 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 opera-
tion the inducer motor IDM comes up to speed, the
low--heat pressure switch LPS closes, and the fur-
nace 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 be-
gin 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 opera-
tion, the inducer motor IDM remains running at
high--speed, and the high--heat pressure switch re-
lay 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 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 maxi-
mum 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 ig-
niter 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 fur-
nace 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 blow-
er--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 Igni-
tion--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 blow-
er--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. Si-
multaneously, the humidifier terminal HUM and electronic
air cleaner terminal EAC--1 are energized and remain ener-
gized throughout the heating cycle.
f.
Switching from Low-- to High--Heat
-- If the furnace con-
trol 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 HP-
SR is de--energized to close the NC contact. When suffi-
cient 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
