Lennox International Inc. 4HP18LT - Manual (Page 20)

506470-01 Issue 1007
System Diagnostic Module
4HP18LT units contain a diagnostic module for
troubleshouting heat pump 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 flashing LED indicator
communicates the failure code.
LED Description
POWER LED (Green) indicates voltage is present at the
power connection of the module.
ALERT LED (Yellow) communicates an abnormal system
condition through a unique flash code. The ALERT LED
will flash a number of times consecutively, pause, and then
repeat the process. The number of consecutive flashes
correlates to a paticular 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
nodule displays the appropriate ALERT and/or TRIP LED.
The yellow ALERT LED will flash a number of times
consecutively, pause, and then repeat the process. To
identify a slash code number, count the number of
consecutive flashes. Refer to Table 10 below and Table 11
on page 20 for information on the flash codes.
Page 20
Table 10
Flash Codes