53
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 humidifier terminal HUM and
electronic air cleaner terminal EAC--1 are energized
and remain 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 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 blower motor
BLWM will transition to high--heat airflow five
seconds after the furnace control CPU switches from
low--heat to high--heat.
g.
Switching from High-- to Low--Heat
--The furnace
control CPU will not switch from high--heat to low--
heat while the thermostat R--to--W circuit is closed
when using a single--stage thermostat.
h.
Blower--Off Delay
--When the thermostat is satisfied,
the R to W circuit is opened, de--energizing the gas
valve GV--M, stopping gas flow to the burners, and
de--energizing the humidifier terminal HUM. The in-
ducer 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 at low--heat airflow or transition to low--heat
airflow for 90, 120, 150, or 180 seconds (depending
on selection at blower--OFF delay switches). The fur-
nace control CPU is factory--set for a 120--second
blower--OFF delay.
2.
Two--Stage Thermostat and Two--Stage Heating
See Fig. 27--34 for thermostat connections.
NOTE
: In this mode the low--heat only switch SW1--2 must be
ON to select the low--heat only operation mode in response to
closing the thermostat R--to--W1 circuit. Closing the thermostat
R--to-- W1--and--W2 circuits always causes high--heat operation,
regardless of the setting of the low--heat only switch.
The wall thermostat “calls for heat”, closing the R--to--W1 circuit
for low--heat or closing the R--to--W1--and--W2 circuits for
high--heat. 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.
The start up and shut down functions and delays described in
item 1. above apply to the 2--stage heating mode as well, except
for switching from low-- to high--Heat and vice versa.
a.
Switching from Low-- to High--Heat
-- If the thermo-
stat R--to--W1 circuit is closed and the R--to--W2 cir-
cuit closes, the furnace control CPU will switch the
inducer motor IDM speed from low to high. 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 ener-
gized. The blower motor BLWM will transition to
high--heat airflow five seconds after the R--to--W2 cir-
cuit closes.
b.
Switching from High-- to Low--Heat
--If the thermo-
stat R--to-- W2 circuit opens, and the R--to--W1 circuit
remains closed, the furnace control CPU will switch
the inducer motor IDM speed from high to low. The
high--heat pressure switch relay HPSR is energized to
open the NC contact and de--energize the high--heat
gas valve solenoid GV--HI. When the inducer motor
IDM reduces pressure sufficiently, the high--heat pres-
sure switch HPS will open. The gas valve solenoid
GV--M will remain energized as long as the low--heat
pressure switch LPS remains closed. The blower motor
BLWM will transition to low--heat airflow five
seconds after the R--to--W2 circuit opens.
3.
Cooling mode
The thermostat “calls for cooling”.
a.
Single--Speed Cooling
--
See Fig. 27 for thermostat connections
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 cooling airflow. Cooling airflow is based
on the A/C selection shown in Fig. 57. 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
circuits are opened. The outdoor unit will stop, and the
furnace blower motor BLWM will continue operating
at cooling airflow for an additional 90 seconds. Jump-
er Y/Y2 to DHUM to reduce the cooling off--delay to
5 seconds. (See Fig. 26.)
b.
Single--Stage Thermostat and Two--Speed Cooling
(Adaptive Mode)
--
See Fig. 34 for thermostat connections.
This furnace can operate a two--speed cooling unit
with a single--stage thermostat because the furnace
control CPU includes a programmed adaptive se-
quence of controlled operation, which selects low--
cooling or high--cooling operation. This selection is
based upon the stored history of the length of previous
cooling period of the single--stage thermostat.
NOTE
: The air conditioning relay disable jumper ACRDJ must
be connected to enable the adaptive cooling mode in response to
a call for cooling. (See Fig. 26.) When ACRDJ is in place the
furnace control CPU can turn on the air conditioning relay ACR
to energize the Y/Y2 terminal and switch the outdoor unit to
high--cooling.
The furnace control CPU can start up the cooling unit in either
low-- or high--cooling. If starting up in low--cooling, the furnace
control CPU determines the low--cooling on--time (from 0 to 20
minutes) which is permitted before switching to high--cooling. If
the power is interrupted, the stored history is erased and the
furnace control CPU will select low--cooling for up to 20 minutes
and then energize the air conditioning relay ACR to energize the
Y/Y2 terminal and switch the outdoor unit to high--cooling, as
long as the thermostat continues to call for cooling. Subsequent
selection is based on stored history of the thermostat cycle times.
The wall thermostat “calls for cooling”, closing the
R--to--G--and--Y circuits. The R--to--Y1 circuit starts the outdoor
unit on low--cooling speed, and the R--to--G--and--Y1 circuits
starts the furnace blower motor BLWM at low--cooling airflow
which is the true on--board CF selection as shown in Fig. 57.
If the furnace control CPU switches from low--cooling to
high--cooling, the furnace control CPU will energize the air
conditioning relay ACR. When the air conditioning relay ACR is
energized the R--to--Y1--and--Y2 circuits switch the outdoor unit
58C
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