Lennox LGT Series Unit Information page 60

Blower Operation:
1 - Line voltage is routed to B3 blower motor through TB2 terminal strip, TB13 terminal strip and J/P48 terminals 1, 2 and 3.
2 - B3 blower motor runs internal diagnostics to check for proper temperature, voltage, etc. (KL2-2 and -3). This process takes approximately 10 seconds. Refer
to the Failure Handling/Troubleshooting section.
3 - A55 Unit Controller receives a thermostat demand. After theA55 proves (P259-7 and -6) that B3 blower motor internal relay (KL2-2 and -3) is closed, B3
blower motor is energized (0-10VDC from P259-4 to KL3-4). B3 blower motor controls are grounded through KL2-2 and -3 to A55 P259-6.
4 - If configured, A55 checks S52 blower proving switch to make sure it closes within 16 seconds of the 0-10VCD signal being sent to B3 blower motor.
Blower Fault Sequence Direct Drive Motor - No S52:
1 - Line voltage is provided to B3 blower motor.
2 - After 10 seconds, the B3 blower motor internal relay does not close.
3 - Alarm 186 is set by the A55 Unit Controller, de-energizing unit. If one of the "Error" failures listed in table 14 occurs ("Warning" failures will not set Alarm
186), service is required. Refer to the Failure Handling/Troubleshooting section.
4 - If B3 blower motor internal relay closes continue to next step.
5 - A55 sends 0-10VDC signal to B3 blower motor.
6 - \During B3 blower motor operation, the internal motor relay opens.
7 - \Alarm 186 is set by A55 and de-energizes the unit. Service is required. Refer to the Failure Handling/Troubleshooting section.
Blower Fault Sequence Direct Drive Motor - With S52 (If Configured):
1 - A55 Unit Controller sends 0-10VDC signal to B3 blower motor.
2 - After 16 seconds, if S52 blower proving switch remains open, A55 will remove 0-10VDC signal for 5 minutes.
3 - A55 sends 0-10VDC signal to B3 blower motor.
4 - After 16 seconds, if S52 blower proving switch remains open, A55 will remove 0-10VDC signal for another 5 minutes.
5 - After the third try, A55 will de-energize the unit. Service is required.
Failure Handling/Troubleshooting:
1 - Follow table 18 to troubleshoot possible failures that would cause Alarm 186 to set.
2 - BEFORE DETERMINING THAT THE BLOWER ASSEMBLY HAS FAILED, use the A55 Unit Controller to clear delays and operate the blower.
3 - Main Menu > Service > Offline > Clear Delays > Yes > Save
4 - Main Menu > Service > Test > Blower
5 - Observe if the blower operates or if Alarm 186 sets again.
6 - If blower does not operate and Alarm 186 is set again, blower assembly must be replaced.
7 - If blower assembly does operate, wait a minimum of 30 minutes to ensure Alarm 186 is not set again.
DIRECT DRIVE BLOWER SEQUENCE OF OPERATION / TROUBLESHOOTING
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