Service Manual

SYSTEM OPERATION
43
FAN ONLY MODE
The normal operational sequence in fan only mode is as
follows:
• R and G thermostat contacts close, initiating a call
for fan.
• Integrated control module performs safety circuit
checks.
• Circulator blower is energized on continuous fan speed
(25, 50, 75, 100% of the furnace’s maximum airflow
capability) following a five (5) second delay. Elec-
tronic air cleaner terminal is de-energized.
• R and G thermostat contacts open, completing the
call for fan.
• Circulator blower is de-energized. Electronic air
cleaner terminal is de-energized.
• Furnace awaits next call from thermostat.
DEHUMIDIFICATION MODE
The normal operational sequence in dehumidification
mode is as follows:
1. R and Y1/G or Y1+Y2/G thermostat contacts close,
initiating a call for cool.
2. Integrated control module performs safety circuit checks.
3. Outdoor fan and compressor are energized to their ap-
propriate speed.
4. Circulator blower is energized on the appropriate cool
speed at the level and time determined by the selected
ramping profile. Electronic air cleaner terminals are en-
ergized with circulator blower.
5. Furnace circulator blower and outdoor cooling unit run
their appropriate speed, integrated control module moni-
tors safety circuits continuously.
6. Dehumidistat opens on humidity rise allowing the fur-
nace circulator blower to operate at 85% of the cooling
speed during combined thermostat call for cooling and
dehumidistat call for dehumidification.
7. Humidistat opens on humidity fall allowing furnace cir-
culator blower to switch back to normal cooling speed.
8. R and Y1/G or Y1+Y2/G thermostat contacts open, com-
pleting the call for cool.
9. Outdoor fan and compressor are de-energized.
10. Circulator blower continues running during a cool off de-
lay period. The OFF delay time and airflow level are de-
termined by the selected ramping profile.
11. Electronic air cleaner terminals and circulator blower
are de-energized.
12. Furnace awaits next call from thermostat.
HEATING - Abnormal Operation
The following presents the probable causes of questionable
furnace operation and how to fix them. Look through the
observation window in the blower access door and make a
note of the error code displayed on the dual 7-segment dis-
play. Next, refer to the Troubleshooting Chart - ComfortNet™
on the following pages for an interpretation of the code dis-
played on the LED's for a description of the problem.
NOTE: Use caution when reading the diagnostic codes from
the furnace control's dual, 7-segment LED's. The position
of the control within the furnace can lead to a misinterpreta-
tion of the error codes. With the control in an orientation as
shown below, codes on the dual, 7-segment LED's are read
left to right.
Memory Card Connector
Dual 7-Segment LED’s
2 Y2
HUM
OG Y1C W1 R
DE
W2
1
1. Internal Control Failure with Integrated Ignition Con-
trol. Check for voltage to the furnace and low voltage at
the control board. Check for blown fuse on the control
board. If the control determines it has an internal fault, it
enters a locked-out state. Any of the situations men-
tioned will cause the dual, 7-segment LED's to be off.
The control board should only be replaced only after all
other checks from the Troubleshooting Chart -
ComfortNet™ have been verified.