Control Module Communication; Communication Failures - Carrier 48LC 04 Controls, Start-Up, Operation And Troubleshooting

ALARM
OR
DESCRIPTION
ALERT
NUMBER
Thermostat Y2 Input Activated without Y1
T411
Activated
Thermostat W2 Input Activated without W1
T412
Activated
Thermostat Y and W Inputs Activated
T413
Simultaneously
Economizer Damper Actuator Out of Calibration
Economizer Damper Actuator Torque Above
Load Limit
Economizer Damper Actuator Hunting
Excessively
Economizer Damper Stuck or Jammed
T414
Economizer Damper Actuator Mechanical Failure
Economizer Damper Actuator Direction Switch
Wrong
Excess Outdoor Air
Economizer Economizing When It Should Not
Economizer not Economizing When it Should
Damper Not Modulating
T415 IAQ Input Out of Range
T416 OAQ Input Out of Range
A420 Supply VFD Fault
LEGEND:
ECB--- Economizer Control Board IGC--- Integrated Gas Controller

Control Module Communication

Red LED
Proper operation of the MBB and ECB control boards can be
visually checked by looking at the red status LEDs. When
operating correctly, the red status LEDs should blink in unison at a
rate of once every 2 seconds. If the red LED on the ECB is not
blinking, check the DIP switch positions on the board. If the red
LEDs are not blinking in unison, verify that correct power is being
supplied to all modules. A blinking red LED at the rate of once per
second means that software is not loaded on the board. Also, be
sure that the board is supplied with the current software. If
necessary, reload current software. A board LED that is lit
continuously should be replaced.
Green LED
The MBB and ECB each have one green LED. The Local
Equipment Network (LEN) LED should always be blinking
whenever power is on. If LEN LED is not blinking, check LEN
connections for potential communication errors (MBB J3, J4, and
J5). Communication between modules is accomplished by a 3-wire
sensor bus. These 3 wires run in parallel from module to module.
The J4 connector on the MBB also provides both power and
Board Serial Num-
Device
ber
Prior to 4702N
MBB
Starting 4702N
Prior to 0803N
ECB
Starting 0803N
Table 6 — ComfortLink Alarm Codes (cont)
ACTION TAKEN BY
CONTROL
Run unit as if Y2 and Y1 are
On
Run unit as if W2 and W1
are On
Run unit in mode activated
first
Alert Generated
Alert Generated
Alert Generated
Alert Generated
Alert Generated
Alert Generated
Alert Generated
Alert Generated
Alert Generated
Alert Generated
No IAQ Operations
No OAQ Operations
Unit Shutdown
MBB --- Main Base Board
Table 7 – LEN and CCN Communication Resistances
(LEN) Resistance between Pins/Connector
Pins 1 to 3 Pins 1 to 2
15K  7.5K 
J3, J4, & J5 J3, J4, & J5
18.9K  9.9K 
J3, J4, & J5 J3, J4, & J5
5.9K  5.2K 
J2 J2
18.9K  9.9K 
J2 J2
RESET
METHOD
Automatic Bad Thermostat or Thermostat Wiring
Automatic Bad Thermostat or Thermostat Wiring
Automatic Bad Thermostat or Thermostat Wiring
Calibrate economizer (E.CAL). If problem still exist then
Automatic
determine what is limiting economizer rotation.
Automatic Actuator load too high. Check damper load.
Automatic Damper position changing too quickly.
No economizer motion. Check damper blades, gears, and
Automatic
actuator.
Automatic Check actuator and replace if necessary.
Automatic Actuator direction control switch (CCW, CW) wrong.
Automatic
Automatic
Automatic
Automatic
Automatic Bad sensor, bad wiring, or sensor configured incorrectly.
Automatic Bad sensor, bad wiring, or sensor configured incorrectly.
Automatic VFD fault occurred, review VFD faults.
OAT --- Outdoor--- Air Thermistor
communication directly to the Scrolling Marquee display. The J5
connector on the MBB provides a LEN interface at the field
connection terminal (TB).
Yellow LED
The MBB has one yellow LED which is used to indicate CCN
communication activity. The Carrier Comfort Network (CCN)
LED will blink during times of network communication.

Communication Failures

If the Scrolling Marquee or Navigator display Communication
Failure or the green or yellow LED's do not flash on the boards
then the problem could be the communication chip on one of the
control boards (MBB or ECB). Disconnect all the LEN and CCN
plugs from the board and use an ohm meter to measure the
resistance on the communication pins of the boards to determine if
the board is bad. If the reading is less than half the value indicated
in Table 7, then the board needs to be replaced.
NOTE: The resistive values should be read when the board is
powered off and the unit is locked out.
(CCN) Resistance between Pins/Connector
Pins 2 to 3 Pins 5 to 7
7.5K  15K 
J3, J4, & J5 J5
9.9K  18.9K 
J3, J4, & J5 J5
5K 
---
J2
9.9K 
---
J2
32
PROBABLE CAUSE
Pins 5 to 6 Pins 6 to 7
7.5K  7.5K 
J5 J5
9.9K  9.9K 
J5 J5
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