40
SUPPLY
AIR
RETURN
AIR
Temperature Rise Measurement
Figure 64
Diagnostics
Accessing the furnace’s diagnostic menu provides access
to the last six faults detected by the furnace. Faults are
stored most recent to least recent, Any consecutively
repeated fault is stored a maximum of three times.
Example: A clogged return air filter causes the furnace limit
to trip repeatedly. The control will only store this fault the
first three consecutive times the fault occurs.
NOTE: It is highly recommended that the fault
history be cleared when performing maintenance
or servicing the furnace.
NORMAL SEQUENCE OF OPERATION
Power Up
The normal power up sequence is as follows:
• 115 VAC power applied to furnace.
• Integrated control module performs internal checks.
• Integrated control module monitors safety circuits
continuously.
• The furnace enters a three minute power up delay to
make sure the system is setup properly. During this
time thermostat calls will not be recognized.
•
Furnace awaits call from thermostat. 7-segment LED’s
display
Id L
while awaiting call from thermostat.
Heating Mode
The normal operational sequence in heating mode is as
follows:
• W thermostat contact closes, initiating a call for heat.
• Integrated control module performs safety circuit
checks.
• Induced draft blower is energized on high speed for a
15-second prepurge.
• Induced draft blower steps to low speed following
prepurge. Low stage pressure switch contacts are
closed.
•
Igniter warm up begins upon Inducer draft blower
step to low speed and presence of closed low stage
that indicates 1/2 cu. ft. per revolution. You will use
this number to calculate the quantity of gas in cubic ft.
if the furnace would consume if it ran steadily for one
hour (3600 seconds).
3. If the 1/2 cu. ft. dial was used, multiply your number
by two. EXAMPLE: If it takes23 seconds to complete
one revolution of the 1/2 ft. dial (23 x 2 = 46).
This tells us that at this rate, it would take 46 seconds to
consume one cu. ft. of gas. 3600 / 46 = 78.
This tells us that in one hour, the furnace would consume
78 cu. ft. of gas. The typical value range for 1 cu. ft.
of natural gas is around 1000 BTU. Check with your
gas utility, if possible. In this example, the furnace is
consuming 78,000 BTUH.
NOTE: The final manifold pressure cannot vary by
more than ± 0.3” w.c. for Natural and
+
0.5” for LP
from the specified setting. Consult your local
gas supplier if additional input rate adjustment is
required.
4. Turn ON gas to and relight all other appliances
turned off in step 1. Be certain that all appliances
are functioning properly and that all pilot burners are
operating.
Temperature Rise
Temperature rise must be within the range specified on the
unit rating plate. An incorrect temperature rise may result
in condensing in or overheating of the heat exchanger.
An airflow and temperature rise table is provided in the
Specification Sheet applicable to your model. Determine
and adjust temperature rise as follows:
1.
Operate furnace with burners firing for approximately
ten minutes. Ensure all registers are open and all
duct dampers are in their final (fully or partially open)
position.
2. Place thermometers in the return and supply ducts as
close to the furnace as possible. Thermometers must
not be influenced by radiant heat by being able to
“see” the heat exchanger.
3. Subtract the return air temperature from the supply
air temperature to determine the air temperature rise.
Allow adequate time for thermometer readings to
stabilize.
4. Adjust temperature rise by adjusting the circulator
blower speed. Increase blower speed to reduce
temperature rise. Decrease blower speed to increase
temperature rise. Refer to
Startup Procedure and
Adjustment -Circulator Blower Speeds
for speed
changing details.
