Lennox S40 - Page 76

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Table 21. Lennox S40 Smart Thermostat Alert Codes and Troubleshooting
E2A=Errors to Action, GF= Gas Furnace, AH=Air Handler, IU=Indoor unit (GF or AH), HP=Heat Pump, AC=Air Conditioner, OU=Outdoor Unit (AC or HP), PA=Pure Air S, ZA=Zone system,
SRS=Smart Room Sensor, TS=Thermostat , IAQ- IAQ Monitor and WE=Wi-Fi Extender
Alert
Code
Inverter
Flash
Code
Priority
Condition
Actual Displayed Alert
Text Under dealer control
center > Notications
Component or System Operational State and Troubleshooting Tip
How to clear
alert code
434 53
Service
Soon/Service
Urgent
OU Inverter
Communication Error
to Main Control
• Outdoor control has lost communications with the inverter continuously during a single thermostat call and
one hour period.
• Outdoor control will stop all compressor demands – service soon condition.
• Indoor blower will stop functioning.
NOTE: Indoor blower will not run in test mode either when alert code 434 is active. Only after system reset
will it operate.
• This alert code will occur if the outdoor unit power is turned off and the indoor unit power (24VAC to
Lennox outdoor control) remains on, or if the indoor unit power is turned off (24VAC to Lennox outdoor
control) and the outdoor unit power is on. This could occur while performing service or maintenance
procedures on the indoor or outdoor unit.
• The Lennox outdoor control will attempt to re-establish communication to the inverter when the alert code
434 occurs by cycling the outdoor unit contactor off for two minutes. Upon energizing the contactor the
Lennox outdoor control will attempt to communicate to the inverter for three minutes. This process will be
repeated three times in attempt to establish communication before locking out.
• If the unit is locked out with a service urgent alert code 434, reset the system by cycling the outdoor unit
power off and back on. Then cycle the indoor power off (24VAC to the Lennox outdoor control) and then
back on.
• If this condition continuously occurs during a one hour period and during a single thermostat call, the
outdoor unit will lock out and display alert code 434 – service urgent condition.
Troubleshooting Options:
• Check for loose or disconnected electrical connections.
• Interruption of main power to inverter.
• Inverter LEDs will ash code 53.
• Refer to the unit service documentation for detailed troubleshooting procedures.
Inverter ash code 53.
The sequence is:
• Red LED: Five Flashes
• Green LED: Three Flashes
NOTE: Inverter normal operations with no error code present is as follows. Red LED is ON and Green LED
is OFF
Automatically clears
when the system
detects that the issue
no longer exists.
If the unit is locked out
with a service urgent
alert code 434, reset
the system by rst
cycling the outdoor unit
power off and back.
Then cycle the indoor
power off (24VAC to
the Lennox outdoor
control) and then back
on.