Carrier 160 Series - Sequence of Operation; Two-Stage Heating (Adaptive Mode) with Single-Stage Thermostat; Two-Stage Thermostat and Two-Stage Heating; Cooling Mode Operation

13. Reconnect wires to the following components (Use con-
nection diagram on wiring label, if wires were not marked
for reconnection locations.):
a. Draft safeguard switch.
b. Inducer motor.
. Pressure switches.
. Limit overtemperature switch.
. Gas valve.
. Hot surface igniter.
. Flame-sensing electrode.
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. Flame rollout switches.
14. Reinstall internal vent pipe, if applicable.
15. Reinstall vent connector on furnace vent elbow. Securely
fasten vent connector to vent elbow with 2 field-supplied,
corrosion-resistant, sheet metal screws located 180° apart.
16. Replace blower access door only if it was removed.
17. Set thermostat above room temperature and check furnace
for proper operation.
18. Verify blower airflow and speed changes between heating
and cooling.
4 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. A fire or explosion may
result causing property damage, personal injury or loss of
life.
19. Check for gas leaks.
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. 53, 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 12 during the 90-second 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 vaive GV.
1. Two-Stage Heating (Adaptive Mode) with Single-Stage
Thermostat
See Fig. 27 - 34 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 Table 10.) 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 wail 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 oper-
ation the inducer motor IDM comes up to speed,
the low-heat pressure switch LPS closes, and the
furnace control CPU begins a 15-second prepur-
ge 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 con-
tinue to run the inducer motor IDM at high-
speed.
(2.) If the furnace control CPU selects high-heat op-
eration, the inducer motor IDM remains running
at high-speed, and the high-heat pressure switch
relay HPSR is de-energized to close the NC con-
tact. 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 furnace control CPU begins a
15-second prepurge period after the low-heat
pressure switch LPS closes. If the high-heat pres-
sure switch HPS fails to close and the low-heat
pressure switch LPS closes, the furnace will oper-
ate at low-heat gas flow rate until the high-heat
pressure switch closes for a maximum of 2 min-
utes 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 prov-
ing period begins. The HSI igniter will remain ener-
gized 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.
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58CV