3. Set thermostat heat anticipator.
a. When using a nonelectronic thermostat, the thermostat heat
anticipation must be set to match the amp draw of the
electrical components in the R-W/W1 circuit. Accurate
amp draw readings can be obtained at the wires normally
connected to thermostat subbase terminals R and W/W1.
Fig. 18 illustrates an easy method of obtaining the actual
amp draw. The amp reading should be taken after the
blower motor has started and the furnace is operating in
low fire. To operate the furnace in low fire, first move
SW-2 to the ON position, THEN connect the ammeter
wires as shown in Fig. 15. The thermostat anticipator
should NOT be in this circuit while measuring the current.
If thermostat has no subbase, the thermostat MUST be
disconnected from the R and W/W1 wires during the
current measurement. Return SW-2 to final desired location
after completing reading. See the thermostat manufactur-
er’s instructions for adjusting the heat anticipator and for
varying the heating cycle length.
b. When using an electronic thermostat, set cycle rate for 3
cycles per hr.
CHECK SAFETY CONTROLS
The flame sensor, gas valve, and pressure switches were all
checked in the Start-Up section as part of normal operation.
1. Check primary limit control.
This control shuts off the combustion control system and
energizes the circulating-air blower motor if the furnace
overheats.
The preferred method of checking the limit control is to
gradually block off the return air after the furnace has been
operating for a period of at least 5 minutes. As soon as the
limit has shut off the burners, the return-air opening should be
unblocked. By using this method to check the limit control, it
can be established that the limit is functioning properly and
will operate if there is a motor failure.
2. Check draft safeguard switch.
The purpose of this control is to permit the safe shutdown of
the furnace during certain blocked vent conditions.
a. Disconnect power to furnace and remove vent connector
from furnace flue collar. Be sure to allow time for vent
connector pipe to cool down before removing.
b. Restore power to furnace and set room thermostat above
room temperature.
c. After normal start-up, allow furnace to operate for 2
minutes, then block flue outlet 100 percent. Furnace should
cycle off within 2 minutes.
d. Remove blockage and reconnect vent connector to furnace
flue collar.
e. Wait 5 minutes and then reset draft safeguard switch.
3. Check flow-sensing pressure switches.
This control proves operation of draft inducer blower.
a. Turn off 115-v power to furnace.
b. Remove gas control door and disconnect inducer motor
lead wires from wire harness.
c. Turn on 115-v power to furnace
d. Close thermostat switch as if making normal furnace start.
If the hot surface ignitor does not glow within several
minutes and control flashes code 32, then the pressure
switches are functioning properly.
e. Turn off 115-v power to furnace.
f. Reconnect inducer motor wires, replace gas control door,
and turn on 115-v power to furnace.
4. Check auxiliary limits.
a. Turn off 115-v power to furnace.
b. Remove blower access door.
c. Disconnect red motor lead at blower speed selector. Mark
terminal for proper reconnection.
d. Replace blower access door.
e. Turn on 115-v power to furnace. Be sure room thermostat
is calling for low heat.
f. Allow furnace to operate until auxiliary limit activates, but
DO NOT operate furnace longer than 4 minutes.
g. If furnace operates for 4 minutes, check/replace limit
switch(es).
h. Turn off 115-v power to furnace.
i. Remove blower access door.
j. Reconnect red motor lead, reset switch, and replace door.
k. Turn on 115-v power to furnace.
CHECKLIST
1. Put away tools and instruments, and clean up debris.
2. Check SW-1 through SW-4 after completing installation to
ensure desired settings for thermostat type (SW-1 and SW-2)
and blower off delay (SW-3 and SW-4). Refer to Tables 6 and
7.
3. Verify manual reset switches have continuity.
4. Ensure blower and gas control access doors are properly
installed.
5. Cycle test furnace with room thermostat.
6. Check operation of accessories per manufacturer’s instruc-
tions.
7. Review User’s Manual with owner.
8. Leave literature packet near furnace.
Fig. 18—Amp Draw Check With Ammeter
A80201
R
Y W G
10 TURNS
THERMOSTAT SUBBASE
TERMINALS WITH
THERMOSTAT REMOVED
HOOK-AROUND
VOLT/AMMETER
EXAMPLE:
5.0 AMPS ON AMMETER
10 TURNS AROUND JAWS
= 0.5 AMPS FOR THERMOSTAT SETTING
FROM UNIT 24-VOLT
TERMINAL BLOCK
17
