Page 14 of 19 506467-01Issue 1946
Operation
System Diagnostic Module
4AC16LT units contain a diagnostic module for
troubleshooting air conditioning system failures. By
monitoring and analyzing data from the compressor and
thermostat demand, the module can accurately detect
the cause of electrical and system related failure without
any sensors. If a system problem occurs, a ashing LED
indicator communicates the failure code.
LED Description
POWER LED (Green) indicates voltage is present at the
power connection of the module.
ALERT LET (Yellow) communicates an abnormal system
condition through a unique ash code. The ALERT LED
will ash a number of times consecutively, pause, and then
repeat the process. The number of consecutive ashes
correlates to a particular abnormal condition.
TRIP LED (Red) indicates there is a demand signal
from the thermostat but no current to the compressor is
detected by the module. The TRIP LED typically indicates
the compressor protector is open or may indicate missing
supply power to the compressor.
Interpreting the Diagnostic LEDs
When an abnormal system condition occurs, the
diagnostic module displays the appropriate ALERT and/or
TRIP LED. The yellow ALERT LED will ash a number of
times consecutively, pause, and then repeat the process.
To identify a ash code number, count the number of
consecutive ashes. Refer to Table 5 for information on
the ash codes.
Every time the module powers up, the last ALERT LED
ash code that occurred prior to shutdown is displayed
for 60 seconds. The module will continue to display the
previous ash code until the condition returns to normal
or 24 VAC is removed from the module. TRIP and ALERT
LEDs ashing at the same time means control circuit
voltage is too low for operation.
24 VAC Power Wiring
The diagnostic module requires a constant nominal 24VAC
power supply. The wiring to the module’s R and C terminals
must be directly from the indoor unit or thermostat.
Thermostat Wiring
The diagnostic module requires a thermostat demand
signal to operate properly. See Figure 7 for connections.
The thermostat signal input is 24VAC and should not be
less than 0.5VAC.
Mis-wired Module Codes
Depending on the system conguration, some ALERT ash
codes may not be active. The presence of safety switches
aects how the system alerts are displayed by the module.
Mis-wiring the diagnostic module will cause false LED
codes. Table 6 describes LED operation when the module
is mis-wired and what troubleshooting action is required to
correct the problem.
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