(See Fig. 10.) Select desired blower motor speed lead from
1 of the other terminals and relocate it to HEAT terminal.
See Table 9 for lead color identification. Reconnect unused
lead on SPARE terminal.
Recheck temperature rise. It must be within the air tempera-
ture rise range specified on furnace rating plate. Recom-
mended operation is at midpoint of rise or above.
3. Set thermostat heat anticipator.
The thermostat heat anticipator must be set to match the amp
draw of the electrical components in the R-W circuit. Accurate
amp draw readings can be obtained at thermostat subbase
terminals R and W. Fig. 14 illustrates an easy method of
obtaining the actual amp draw. The amp reading should be
taken after the blower motor has started. See the thermostat
manufacturer’s instructions for adjusting the heat anticipator
and for varying the heating cycle length.
NOTE:
When using an electronic thermostat, set the cycle rate for
3 cycles per hr.
CHECK SAFETY CONTROLS — The flame sensor, gas valve,
and pressure switch were all checked in the Start-up Procedures
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 functions and operates
properly if there is a motor failure.
2. Check blocked vent safeguard switch.
The purpose of this control is to cause 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 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 collar 100 percent. Furnace should
cycle off within 2 minutes.
d. Remove blockage and reconnect vent pipe to furnace flue
collar.
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Fig. 12—Redundant Automatic Gas Control
Valve
A00238
Fig. 13—Burner Flame
A89020
,
,
BURNER FLAME
BURNER
MANIFOLD
Table 9—Speed Selector
COLOR
SPEED
FACTORY-
ATTACHED TO
Black
High
Cool
Yellow (When
present)
Medium-High
Spare
Blue
Medium-Low
Heat
Red
Low
Spare
White
Common
L2/COM
Fig. 14—Amp Draw Check With Ammeter
A96316
R
Y W G
10 TURNS
THERMOSTAT SUBBASE
TERMINALS WITH
THERMOSTAT REMOVED
(ANITICIPATOR, CLOCK, ETC.,
MUST BE OUT OF CIRCUIT.)
HOOK-AROUND
AMMETER
EXAMPLE:
5.0 AMPS ON AMMETER
10 TURNS AROUND JAWS
=
0.5 AMPS FOR THERMOSTAT
ANTICIPATOR SETTING
FROM UNIT 24-V
CONTROL TERMINALS
17
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