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EXAMPLE: (High-heat operation at 0—2000 ft altitude)
Furnace input from rating plate is 100,000 Btuh
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 975 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 70 sec
Gas rate = 103 cu ft/hr (from Table 13)
Btu heating input = 103 X 975 = 100,425 Btuh
In this example, the orifice size and manifold pressure
adjustment is within ±2 percent of the furnace input rate.
NOTE: Measured gas inputs (high heat and low heat) must be
within ±2 percent of that stated on furnace rating plate when
installed at sea level or derated per that stated above when installed
at higher altitudes.
n. Remove jumper across R, W/W1, and W2 thermostat
connections to terminate call for heat.
B. Set Temperature Rise
CAUTION: 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
temperature from supply-air temperature to determine air
temperature 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 restric-
tions 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 H and
later.
C. 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.
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. 60—Inducer Housing Drain Tube
A99118
Fig. 61—Filling Condensate Trap
A99119
—42—
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