18
verts it to a three phase supply to operate the draft inducer
at the desired speed. The windings of the induced draft
motor will have equal resi/- 5%. Normal resistance
readings at room temperature will range from 14-17 ohms.
The voltage supplied by the IFC to drive the induced draft
blower will vary from 15-110 volts A/C between any two
windings. This would be read between any two of the three
power wires between the IFC and the induced draft blower.
This voltage to the IBD will vary between furnace models
and is dependant on what percentage of maximum fire is
being called for. The power wires are colored red, white,
and black. A green colored ground wire is also present.
Hot Surface Igniter
Modulating furnaces use a 115 volt silicon nitride hot sur-
face igniter. This is the familiar and reliable 0131F00008S
igniter with 17 second warm up time. At room temperature
the igniter has a resistance range of 37 - 68 ohms. The
H.S.I. is connected electrically to the IFC by a 3/16" push-
on connection.
Gas Valve
Modulating furnaces use a 24 VAC pneumatically operated
gas valve by Honeywell. The valve is energized by the inte-
grated furnace control on a call for heat, wired in series
through the front-cover pressure switch. The firing rate per-
centage is determined by the negative pressure created by
the operation of the draft inducer.
Inductor Coil
Wired in series with ¾ and 1 HP ECM motors; the inductor
coil conditions the power supply to the motor, smoothing
out spikes and electrical noise. With voltage applied to one
side of the inductor coil, the output voltage to the motor
should be the same as incoming voltage.
Integrated Furnace Control (IFC)
The IFC is the main control center for the furnace. It has
many functions including;
•
Receiving commands from the thermostat for heat-
ing, and cooling, continuous fan operation.
•
Receiving commands for dehumidification and humidi-
fication.
•
Communicating with the ECM motor for proper air
delivery to the conditioned space.
•
Assuring safe ignition by checking the state of pres-
sure switches and limit switches before and after ig-
nition.
•
Assuring safe operation by continuously monitoring
the presence of flame, the state of the pressure
switches and limit and roll out switches.
•
Displays information on the dual seven segment dis-
plays regarding thermostat call, air flow delivery and
fault status
•
Controlling the speed of the induced draft blower by
variable voltage & frequency.
Features of the IFC:
Aux Terminals Located next to the low voltage connector,
there are two terminals labeled aux in & aux out. A factory
jumper is installed between these two terminals. As an op-
tion; the jumper may be removed and the terminals wired
up to a normally closed float switch. The switch must be
closed for normal operation. If the switch is sensed open,
the IFC will:
•
Terminate a call for gas heat.
•
When the modulating furnace is installed with a com-
municating thermostat and a non-communicating a/
c unit, the IFC will open the Y1 relay to turn off the
condensing unit
•
Log and display an auxiliary open error code
•
Once the auxiliary switch re-closes the IFC reverts
back to normal operation
Hum Terminals A pair of ¼” HUM terminals are located on
the board to power a humidifier. These are dry contacts
rated at 1 amp. A typical application of these contacts would
be to supply one of the Hum contacts with power from the
L1 terminal and connect the remaining Hum terminal to a
humidifier transformer primary. When used with the
CTK02**, CTK03 and CTK04 thermostats, these contacts will
close with a call for humidity and the furnace indoor blower
will be powered at continuous fan speed. When used with a
24 volt control system, the Hum contacts will close on a call
for heat when the induced draft blower is powered.
EAC Terminal A ¼” EAC terminal is provided. Any time
the indoor blower motor is powered, the EAC terminal will
be powered. Contact is rated for 1 amp
Flame Proving. Flame signal is continuously monitored by
the IFC. The flame rod, flame rod wire and proper ground-
ing are all critical to proving the presence of flame. Be-
cause of the design of the Honeywell flame proving system,
reading flame signal with a microamp meter will not pro-
vide reliable and consistent results and is therefore not a
recommended practice. The IFC has a built in warning (E6)
if flame signal is approaching the low threshold.
Field Test Mode This feature can be used by the service
technician to quickly bring a furnace up to high fire. Enter-
ing field test mode will by-pass the staging routine and al-
low the furnace to run at 100% of rated input. To use field
test mode; during a call for heat, press the fault recall but-
ton twice within 5 seconds, the display will change to Ft,
then press and hold the fault recall button for a few seconds
until the display flashes Ft. The furnace will stay in field
test mode for 5 minutes or until the call for heat is re-
moved.
Dual 7 Segment Displays The modulating furnace IFC has
dual 7 segment displays to provide service information. This
information includes; present thermostat demand, CFM, and
fault codes.
PRODUCT DESIGN
