Blower Runs Continuously Q" Motor; Supply Air Blower Does Not Run; Abnormal Sounds; Unit Does Not Shut Off - Lennox G21Q3-40 Unit Information

D − Blower Runs Continuously Q" Motor
1 − Is thermostat blower switch set to ON?" If so,
switch to AUTO."
2 − Is blower control OFF" setting below ambient air tem
perature? If so, readjust to 90 °F.
3 − Is primary blower control operating normally? Re
place if necessary.
4 − Are blower relay contacts operating normally? Re
place if necessary.
E − Supply Air Blower Does Not Run
Q" Motor
1 − Check the voltage at the blower motor taps after
about 45 seconds.
2 − Check for loose wiring.
3 − Is blower relay operating properly? Check for 120
VAC between terminal 2 and neutral immediately af
ter ignition. See electrical schematic.
4 − Is fan time control relay K36 operating properly?
Check for 120VAC between terminal NO" (nor
mally open) and neutral after the unit has been
operating 45 seconds. See electrical schematic.
5 − Blower motor and /or capacitor operating normal
ly? Check 120 VAC between the heating motor tap
and neutral after the unit has been operating 45
seconds. See electrical schematic. Use standard
motor troubleshooting techniques if voltage reach
es this point and blower still operates.
F − Unit Does Not Shut Off
1 − Is thermostat operating normally?
a − Check for shorted 24 VAC control circuit wir
ing. Repair or replace if necessary.
2 − Is the gas valve stuck open?
G − Abnormal Sounds
Corrective action is required if abnormal hissing
sounds around the air decoupler are heard. This
problem may be caused by:
1 − Air leakage around decoupler box cover.
2 − Air leakage around air decoupler box cover mount
ing screws.
3 − Air leakage out of the purge blower lead strain re
lief.
4 − Air leakage around the intake air connection to the
air decoupler box.
5 − Air leakage out of the back of the air decoupler box
around the air intake pipe or the air decoupler box
rear mounting bolts.
The unit should be examined visually for unusual
amounts of condensate in any areas other than the
condensing coil outlet which might indicate a sys
tem leak.
Abnormal rattling and casing vibration other than ob
vious loose parts may indicate metal to metal con
tact of components which are normally separated
during operation. Gas piping, condensing coil outlet
and air intake pipe areas should be checked. Com
bustion chamber to exhaust decoupler area should
also be checked.
Extremely loud pulse" sounds, which can be eas
ily heard through the supply or return air ducts,
may indicate a combustion chamber or tailpipe
leak. Locate and correct combustion chamber or
tailpipe leak before allowing unit to operate.
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