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.
5. Blower-On Delay-If burner flame is proven the blower motor
BLWM is energized 66 sec after gas valve GV-M is opened.
Low-heat-The blower motor BLWM is energized at LO
HEAT speed.
Hi-heat-The BLWM is energized at HI HEAT speed.
Simultaneously, the electronic air cleaner terminal EAC-1 is
energized and remains energized as long as the blower motor
BLWM is energized.
6. 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 switch to HI HEAT speed five seconds
after the furnace control CPU switches from low-heat to
high-heat.
7. Switching From High- To Low- Heat-The control CPU will
not switch from high-heat to low-heat while the thermostat
R-to-W circuit is closed when a single-stage thermostat is
used.
8. 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 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 energized for 90, 120, 150, or 180 seconds (depending
on selection at blower-OFF delay switches). The furnace
control CPU is factory-set for a 120-second blower-OFF
delay.
TWO-STAGE HEATING WITH TWO-STAGE THERMOSTAT
(NON-ADAPTIVE HEATING MODE)
(See Fig. 28 and 52A-G for thermostat connections).
NOTE:
In this mode, the low-heat only switch 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 shutdown functions and delays described in item
1 above apply to 2-stage heating mode as well, except for
switching from low- to high-heat and vice versa.
1. Switching From Low- To High- Heat-If the thermostat R to
W1 circuit is closed and the R to W2 circuit 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 pres-
sure 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 switch to HI HEAT speed five
seconds after the R to W2 circuit closes.
2. Switching From High- To Low- Heat- If the thermostat 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 pressure
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 switch to LO
HEAT speed five seconds after the R to W2 circuit opens.
COOLING MODE
The thermostat “calls for cooling”
1. Single-Speed Cooling
(See Fig. 27 or 28 and 52A, C, or E for thermostat connec-
tions.)
The thermostat closes R-to-G-and-Y circuits. The R-to-Y
circuit starts the outdoor unit, and 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-v when 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 furnace blower motor
BLWM will continue operating on COOL speed for an
additional 90 sec. Jumper Y/Y2 to DHUM to reduce the
cooling off-delay to 5 seconds. (See Fig. 32.)
2. Two-Speed Cooling and Single-Stage Thermostat
(Adaptive Mode)
(See Fig. 27 and 52A-H 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 sequence of controlled
operation, which selects low-cooling or high-cooling op-
eration. 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. 32.) When 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-cool speed (same
speed as LO HEAT).
39
