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Fig. 60—Inducer Housing Drain Tube
Fig. 61—Filling Condensate Trap
n. Remove jumper across R, W/W1, and W2 thermostat
connections to terminate call for heat.
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A99118
A99119
43
SET TEMPERATURE RISE
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Temperature rise must be within limits specified on unit
rating plate. Operation is within a few degrees of midpoint of
rise range when setup switch SW1-4 is OFF. Failure to follow
this caution may result in overheating the heat exchangers or
condensing flue gas in heat exchanger areas not designed for
condensate.
Furnace must operate within ranges of temperature rise specified
on the furnace rating plate. Determine air temperature rise as
follows:
1. Place thermometers in return and supply ducts as near furnace
as possible. Be sure thermometers do not see heat exchanger
so that radiant heat does not affect readings. This practice is
particularly important with straight-run ducts.
2. When thermometer readings stabilize, subtract return-air tem-
perature from supply-air temperature to determine air tem-
perature rise.
NOTE: Temperature rise can be determined for low-heat opera-
tion by placing setup switch SW1-2 on furnace control in ON
position. For high-heat operation, place setup switch SW1-2 in
OFF position and jumper R-W2 on furnace control. DO NOT
forget to return setup switch to OFF position and remove R-W2
jumper upon completion of testing. (See Fig. 32 for switch and
terminal location.)
3. This furnace is capable of automatically providing proper
airflow to maintain the temperature rise within the range
specified on furnace rating plate. If temperature rise is outside
this range, proceed as follows:
a. Check gas input for low- and high-heat operation.
b. Check derate for altitude if applicable.
c. Check all return and supply ducts for excessive restrictions
causing static pressure greater than 0.5-in. wc.
d. Ensure Low Heat Rise Adjust switch SW1-3 on furnace
control is in ON position when a bypass humidifier is used.
(See Fig. 32 for switch location.)
e. Check Troubleshooting Guide for Variable-Speed 2-Stage
Electronic Condensing Furnaces Series 170 and later.
SET THERMOSTAT HEAT ANTICIPATOR
When using a non-electronic thermostat, the thermostat heat
anticipator must be set to match the amp draw of components in
the R-W/W1 circuit. Accurate amp draw measurements can be
obtained only at the thermostat subbase terminals R and W.
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The thermostat and anticipator should NOT be in the circuit while
measuring current. If thermostat has no subbase, the thermostat
must be disconnected from R and W/W1 wires during current
measurement.
Fig. 65 illustrates an easy method of obtaining thermostat amp
draw measurements. The amp reading should be taken after blower
motor has started and furnace is operating in low-heat.
1. To operate furnace in low-heat, turn setup switch SW1-2 to
ON position (See Fig. 32) and connect ammeter leads across
thermostat subbase R-W.
2. See thermostat manufacturer's instructions for adjusting the
heat anticipator and for varying heating cycle length.
NOTE: When using an electronic thermostat, set cycle rate for 3
cycles per hr.
3. Return setup switch SW1-2 to OFF position and replace
thermostat on subbase.
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