International comfort products N8MXL Installation Instructions Manual page 33

6. Set thermostat heat anticipator.
a. Mechanical thermostat − Set thermostat heat anticip-
ator to match the amp. draw of the electrical compon-
ents in the R−W circuit. Accurate amp. draw readings
can be obtained at the wires normally connected to
thermostat subbase terminals, R and W. The thermo-
stat anticipator should NOT be in the circuit while
measuring current.
(1.) Remove thermostat from subbase or from wall.
(2.) Connect an amp. meter as shown in Figure 43
across the R and W subbase terminals or R and
W wires at wall.
(3.) Record amp. draw across terminals when fur-
nace is in heating and after blower starts.
(4.) Set heat anticipator on thermostat per thermostat
instructions and install on subbase or wall.
b. Electronic thermostat: Set cycle rate for 4 cycles per
hr.
7. Adjust heat off delay The heat off delay has 4 ad-
justable settings from 90 sec to 180 sec. The heat off
delay jumpers are located on the furnace control board.
(See Figure 25) To change the heat off delay setting,
move the jumper from one set of pins on the control to
the pins used for the selected heat off delay. Factory
heat off delay setting is 120 sec.
8. Set airflow CFM for cooling Select the desired blower
motor speed lead for cooling airflow. See Table 5−Air
Delivery−CFM (With Filter) for lead color identification.
Step 4 —Check Safety Controls
The flame sensor, gas valve, and pressure switch were all
checked in the Start−up procedure section as part of normal
operation.
1. Check Main Limit Switch(es)
This control shuts off combustion control system and
energizes air−circulating blower motor, if furnace over-
heats. By using this method to check limit control, it can
be established that limit is functioning properly and will
operate if there is a restricted duct system or motor fail-
ure. If limit control does not function during this test,
cause must be determined and corrected.
a. Run furnace for at least 5 minutes.
b. Gradually block off return air with a piece of cardboard
or sheet metal until the limit trips.
c. Unblock return air to permit normal circulation.
d. Burners will re−light when furnace cools down.
2. Check draft safeguard switch.
The purpose of this control is to cause the safe shut-
down of the furnace during certain blocked vent condi-
tions.
a. Verify vent pipe is cool to the touch.
b. Disconnect power to furnace and remove vent con-
nector from furnace vent elbow.
c. Restore power to furnace and set room thermostat
above room temperature.
d. After normal start−up, allow furnace to operate for 2
minutes, then block vent elbow in furnace 80 percent
of vent area with a piece of flat sheet metal.
e. Furnace should cycle off within 2 minutes. If gas does
not shut off within 2 minutes, determine reason draft
safeguard switch did not function properly and correct
condition.
f. Remove blockage from furnace vent elbow.
g. Switch will auto−reset when it cools.
441 01 1421 01
h. Re−install vent connector.
NOTE: Should switch remain open longer than 3 minutes,
furnace control board will lockout the furnace for 3 hours. To
reset furnace control board, turn thermostat below room
temperature or from HEAT to OFF and turn 115v power OFF,
then back ON.
Figure 43 − Amp. Draw Check with Ammeter
EXAMPLE: 5.0 AMPS ON AMMETER
3. Check Pressure Switch
This control proves operation of the draft inducer
blower.
a. Turn off 115−v power to furnace.
b. Disconnect inducer motor lead wires from wire har-
c. Turn on 115−v power to furnace.
d. Set thermostat to "call for heat" and wait 1 minute.
e. Determine reason pressure switch did not function
f. Turn off 115−v power to furnace.
g. Reconnect inducer motor wires, replace outer door,
h. Blower will run for 90 sec and flash status code 1+2
i. Furnace should ignite normally.
Step 5 —Checklist
1. Put away tools and instruments. Clean up debris.
2. Verify that heat off−delay time is selected as desired.
3. Verify that blower and burner access doors are prop-
erly installed.
4. Cycle test furnace with room thermostat.
5. Check operation of accessories per manufacturer's in-
structions.
6. Review User's Guide with owner.
7. Attach literature packet to furnace.
Specifications are subject to change without notice.
THERMOSTAT SUBBASE
TERMINALS WITH
THERMOSTAT REMOVED
(ANITICIPATOR, CLOCK, ETC.,
MUST BE OUT OF CIRCUIT.)
HOOK-AROUND
AMMETER
R Y W G
10 TURNS
FROM UNIT 24-V
CONTROL TERMINALS
= 0.5 AMPS FOR THERMOSTAT
ANTICIPATOR SETTING
10 TURNS AROUND JAWS
ness.
When pressure switch is functioning properly, hot sur-
face igniter should NOT glow and control flashes a
status code 3. If hot surface igniter glows when inducer
motor is disconnected, shut down furnace immedi-
ately.
properly and correct condition.
and turn on 115−v power.
before beginning the call for heat again.
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