32
18-CD20D3-18
Installer’s Guide
Turn on the main electrical supply and set the thermostat
above the indicated temperature. The ignitor will automati-
cally heat, then the gas valve is energized to permit the flow
of gas to the burners. After ignition and flame is established,
the flame control module monitors the flame and supplies
power to the gas valve until the thermostat is satisfied.
TO SHUT OFF
For complete shutdown: Turn the gas cock knob on the main
gas valve to the “OFF” position (See Figures 41-43). Discon-
nect the electrical supply to the unit.
▲
CAUTION
!
If this is done during the cold weather months, provisions
must be taken to prevent freeze-up of all water pipes and
water receptacles.
Whenever your house is to be vacant, arrange to have
someone inspect your house for proper temperature.
This is very important during freezing weather. If for
any reason your furnace should fail to operate damage
could result, such as frozen water pipes.
SEQUENCE OF OPERATION
Thermostat call for heat (2-stage thermostat)
Call for 1st stage only:
W1 thermostat contacts close signaling the control module to
run its self-check routine. After the control module has
verified that the 1st stage pressure switch contacts are open
and the limit switch(es) contacts are closed, the draft blower
will be energized.
As the induced draft blower comes up to speed, the pressure
switch contacts will close and the ignitor warm up period will
begin. The ignitor will heat for approx. 20 seconds, then the
gas valve is energized in 1st stage to permit gas flow to the
burners.
The flame sensor confirms that ignition has been achieved
within the 4 second ignition trial period.
As the flame sensor confirms that ignition has been achieved,
the delay to fan ON period begins timing and after approx.
45 seconds the indoor blower motor will be energized at low
speed and will continue to run during the heating cycle.
Call for 2nd stage after 1st stage:
W2 thermostat contacts close signaling a call for 2nd stage
heat. After a 30 second delay, the induced draft blower will
be energized on high speed and the 2nd stage pressure
switch contacts will close. The gas valve is energized in 2nd
stage and the indoor blower motor in high speed.
2nd stage satisfied, 1st stage still called:
W2 thermostat contacts open signaling that 2nd stage
heating requirements are satisfied.
The induced draft blower is reduced to low speed allowing the
2nd stage pressure switch contacts to open and the gas valve
is reduced to 1st stage. The indoor blower motor is reduced
to low speed.
1st stage satisfied:
W1 thermostat contacts open signaling that 1st stage
heating requirements are satisfied. The gas valve will close
and the induced draft blower will be de-energized. The
indoor blower motor will continue to run for the fan off period
(Field selectable at 60, 100, 140 or 180 seconds), then will be
de-energized by the control module.
Thermostat call for heat (1-stage Thermostat)
W1/W2 (jumpered) thermostat contacts close signaling a call
for heat. 1st stage sequence of operation remains the same as
above. 2nd stage heat will energize after the stage delay
timer (field selectable at .5, 5, 10 or 15 minutes) has expired.
Thermostat satisfied:
W1/W2 (jumpered) contacts open signaling the control
module to close the gas valve. The induced draft blower is
switched to low speed and de-energized after the post purge
timer has expired. The indoor blower motor will continue to
operate after the flames are extinguished and then is
switched to low heat speed for the FAN-OFF period.
CONTROL AND SAFETY SWITCH
ADJUSTMENTS
LIMIT SWITCH CHECK OUT
The limit switch is a safety device designed to close the gas
valve should the furnace become overheated. Since proper
operation of this switch is important to the safety of the unit,
it
must be checked out on initial start up by the installer.
To check for proper operation of the limit switches, set the
thermostat to a temperature higher than the indicated
temperature to bring on the gas valve. Restrict the airflow
by blocking the return air (disconnecting the indoor blower
may trip the inducer limit). When the furnace reaches the
maximum outlet temperature as shown on the rating plate,
the burners must shut off. If they do not shut off after a
reasonable time and overheating is evident, a faulty limit
switch is probable and the limit switch must be replaced.
After checking the operation of the limit control, be sure to
remove the paper or cardboard from the return air inlet.
Refer to Service Facts for additional instructions.
AIRFLOW ADJUSTMENT
Check inlet and outlet air temperatures to make sure they
are within the ranges specified on the furnace rating name-
plate. If the airflow needs to be increased or decreased, see
the Airflow Label on the furnace or the unit’s Service Facts
for information on changing the speed of the blower motor for
your specific model. Blower speed changes are made on the
Integrated Furnace Control (IFC).
There is a bank of 8 dip switches located near the thermostat
connections to the Integrated Furnace Control. The dip
switches work in pairs to match the airflow for the outdoor
unit size (tons), cooling airflow adjustment, cooling off-delay
options, and furnace heating airflow adjustment.
▲
WARNING
!
Disconnect power to the unit before removing the blower
door. Allow a minimum of 10 seconds for IFC power supply
to drain to 0 volts. Failure to follow this warning could
result in property damage, personal injury or death.
INDOOR BLOWER TIMING
Heating:
The integrated furnace control module controls the
indoor blower. The blower start is fixed at 45 seconds after
ignition. The FAN-OFF period is field selectable by dip
switches SW-2, #1 and #2 at 60, 100, 140, or 180 seconds.
The factory setting is 100 seconds.
W1-W2 stage delay (jumpered together) is field selectable by
dip switch SW-1, #1 and #2 at .5, 5, 10 or 15 minutes. The
factory setting is 10 minutes. (See wiring diagram).
Cooling:
The fan delay-off period is set by dip switches on the
Integrated Furnace Control. The options for cooling delay off
is field selectable by dip switches #5 and #6.
