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Adjust Temperature Rise
NOTE: Blower door must be installed when taking temperature
rise reading. Leaving blower door off will result in incorrect
temperature measurements, due to possible changes in duct static
pressure and airflow.
CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in:
S Overheating the heat exchangers or condensing flue gases
in heat exchanger areas not designed for condensate.
S Shortened furnace life.
S Component damage.
Temperature rise must be within limits specified on furnace
rating plate. Recommended operation is at midpoint of rise
range or slightly above.
Jumper R to W to check gas- -heat temperature rise. Do not exceed
temperature rise ranges specified on unit rating plate.
This furnace must operate within the temperature rise ranges
specified on the furnace rating plate. Determine the air temperature
as follows:
1. Place duct thermometers in return and supply ducts as close
to furnace as possible. Be sure thermometers do not "see"
heat exchangers so that radiant heat does not affect
thermometer readings. This is particularly important with
straight run ducts.
2. When thermometer readings stabilize, subtract return- -air
temperature from supply- -air temperature to determine
temperature rise.
If the temperature rise is outside this range, check the following:
1. Gas input rate.
2. Derate for altitude, if applicable.
3. Return and supply ducts for excessive restrictions causing
static pressures greater than 0.50- -in. w.c. (125 Pa)
4. Adjust temperature rise by adjusting blower speed.
S Increase blower speed to reduce temperature rise.
S Decrease blower speed to increase temperature rise.
WARNING
!
ELECTRICAL OPERATION HAZARD
Failure to follow this warning could result in personal injury
or death.
Disconnect 115vac electrical power before changing speed tap.
(Read following caution before changing taps).
CAUTION
!
UNIT DAMAGE HAZARD
To avoid operating outside the rise range and avoid
component damage:
Refer to the Air Delivery Tables to determine which airflows
and settings are allowed for proper heating airflow. DO NOT
use the highlighted settings for Heating airflow. The
highlighted settings are to be used for Cooling and
Continuous Fan ONLY.
Change these settings as required to maintain proper temperature
rise for Heating and Cooling as described above. To change blower
motor speed selections for heating mode, remove blower motor
lead from control HEAT terminal. See Fig. 39. Select desired
blower motor speed lead from one of the other motor leads and
relocate it/them to HEAT (heating blower tap) terminal(s).
Reconnect original lead on SPARE terminal.
Adjust Blower Off Delay (Heat Mode)
If desired, the main blower off time delay period may be
lengthened or shortened when operating in the heating mode to
provide greater comfort. For position and location of jumpers on
control center, see Fig. 39 and 71.
The blower off delay has four adjustable settings from 90 sec to
180 sec. See Table 18. To change the blower off delay setting,
move the jumper from one set of pins on the control to the pins
used for the desired blower off delay. Factory blower off delay
setting is 120 sec.
Table 18 – Blower Off Delay Jumper Positions
PINS
1 AND 2
Time (in sec.)
90
Adjust Cooling Airflow
The cooling airflow can be set from the remaining blower speed
taps. Refer to the Air Delivery Tables in these instructions.
CAUTION
!
FURNACE OVERHEATING HAZARD
Failure to follow this caution may result in reduced furnace
life.
Recheck temperature rise. It must be within limits specified
on the rating plate. Recommended operation is at the
mid- -point of rise range or slightly above.
Adjust Thermostat Heat Anticipator
Mechanical thermostat: Set thermostat heat anticipator to match
the amp draw of the electrical components in the R- -W circuit.
Accurate amp draw readings can be obtained at the wires normally
connected to thermostat subbase terminals R and W.
thermostat anticipator should NOT be in the circuit while
measuring current.
1. Remove thermostat from subbase or from wall.
2. Connect an amp meter across the R and W subbase termi-
nals or R and W wires at wall.
3. Record amp draw across terminals when furnace is in low
heat and after blower starts.
4. Set heat anticipator on thermostat per thermostat instruc-
tions and install on subbase or wall.
5. Install blower access door.
Electronic thermostat: Set 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 procedure section as part of normal operation.
1. Check Main Limit Switch
This control shuts off combustion system and energizes air- -
circulating blower motor, if furnace overheats. By using this
method to check the temperature limit control, it can be es-
tablished that the limit is functioning properly and that the
limit will operate if there is a restricted return- -air supply or
motor failure. If the limit control does not function during
this test, the 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.
64
2 AND 3
3 AND 4
4 AND 5
120
150
180
The
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