Service Manual

SYSTEM OPERATION
56
bank of two dipswitches that provide termination functions
for the communications transmission lines. Communica-
tions errors will result if these switches are not correctly
set. The table below indicates the switch position for the
bias and termination dipswitches along with the expected
voltages. Note that the ON position is the correct position
for all bias and termination dipswitches.
The ComfortNet system is a fully communicating system,
and thus, constitutes a network. Occasionally the need to
troubleshoot the network may arise. The integrated furnace
control has some on-board tools that may be used to trouble-
shoot the network. These tools are: red communications
LED, green receive (Rx) LED, and learn button.
• Red communications LED – Indicates the status of
the network. The table below indicates the LED
status and the corresponding potential problem.
• Green receive LED – Indicates network traffic. The
table below indicates the LED status and the corre-
sponding potential problem.
• Learn button – Used to reset the network. Depress
the button for approximately 2 seconds to reset the
network.
ComfortNet™ System
Submenu Item User Modifiable Options Comments
Cool Airflow (CL CFM) 18, 24, 30, 36, 42, 48, or 60, default
is 18
Selects the airflow for the non-CT
compatible single stage AC unit
Cool Airflow Trim (CL TRM) -10% to +10% in 2% increments,
default is 0%
Selects the airflow trim amount for the non-
communicating compatible single stage AC
unit
Cool Airflow Profile (CL PRFL) A, B, C, or D, default is A Selects the airflow profile for the non-
communicating compatible single stage AC
unit
Cool ON Delay (CL ON) 5, 10, 20, or 30 seconds, default is
5 sec onds
Selects the indoor blower ON delay for the
non-communicating compatible single
stage AC unit
Cool OFF Delay (CL OFF) 30, 60, 90, or 120 seconds, default
is 30 s econds
Selects the indoor blower OFF delay for the
non-communicating compatible single
stage AC unit
NON-COMM (APPLIES ONLY TO A COMMUNICATING COMPATIBLE FURNACE MATCHED
WITH A NON-COMMUNICATING COMPATIBLE SINGLE STAGE AIR CONDITIONER)
DIAGNOSTICS
Accessing the furnace’s diagnostics menu provides ready
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. Navigate to the diag-
nostics menu as described above in Accessing and Navi-
gating the Advanced Features Menus.
NOTE: It is highly recommended that the fault history be
cleared when performing maintenance or servicing the
furnace.
NETWORK TROUBLESHOOTING
Communications is achieved by taking the difference between
two dc signals. The signals and transmission lines are re-
ferred to as “data 1” and “data 2”. Each transmission line is
biased to approximately 2.5Vdc. During data reception/trans-
mission, the data lines vary between +5V and ground. (When
data 1 is increasing towards +5V, data 2 is decreasing to-
wards ground and when data 1 is decreasing towards ground,
data 2 is increasing towards +5V. Typically, the data 1 line
is approximately 2.6Vdc and the data 2 transmission line is
approximately 2.3Vdc. The voltage difference between data
1 and data 2 is typically 0.2 to 0.6 Vdc.
The indoor control is equipped with a bank of three
dipswitches that provide biasing and termination functions
for the communications transmission lines. The outdoor
control in the ComfortNet compatible unit is equipped with a
Submenu Item Indication (for Display Only; not User Modifiable)
Mode (MODE) Displays the current furnac e operating mode
CFM (CFM) Displays the airflow for the current operating mode
STATUS