Lennox air conditioner troubleshooting

If any of the following conditions exist, immediately turn the system (indoor and outdoor
units) off at the unit disconnect switch and call a licensed professional technician, or equiva-
lent, for repairs
– There is a very loud sound during unit operation.
– There is a terrible odor coming from the indoor unit during operation.
– Water is leaking into the room.
– The circuit breaker trips frequently.
– Water or some other liquid has been splashed into the indoor unit.
If none of the above conditions exist, check the following items before calling for repairs.
Lennox air conditioner troubleshooting

ProblemPossible Cause
Unit does not operate immediately when restarted.Unit control initiates a 3−minute delay at the end of each cycle to protect the compressor from dam-
A whoosh or gurgling noise can be heard at the
indoor unit
Sometimes, the refrigerant can be heard in the
indoor coil when the outdoor unit starts or stops
operation. This is not a malfunction.
Mist is coming out of the indoor unit during cooling
This sometimes happens when the indoor temper-
ature and humidity are very high and the air is be-
ing cooled quickly. The mist will disappear as the
indoor temperature and humidity are lowered
A creaking or popping noise can be heard when
the unit starts or stops
The plastic components of the indoor units some-
times expand and contract when they are heated
and cooled
Unit is not operatingAre the TIMER ON and TIMER OFF features be-
ing used incorrectly?
Is power disconnected or has circuit breaker
Is power shut down?
System is not cooling (or heating) efficientlyIs temperature setting correct?
Are either the air inlet or air outlet blocked on the
outdoor or indoor unit?
Is filter dirty?
Is fan at low speed?
Are windows and doors properly shut?
Wireless remote is not workingIs remote in direct line of sight with indoor unit in-
frared receiver? Has the remote been damaged?
Remove remote control batteries for 30 seconds,
then reinsert them. Replace batteries, if neces-
Water is leaking from indoor unit.Indoor humidity level is very high and water is be-
ing blown from indoor coil. This will stop as humid-
ity level is reduced
Water is leaking from condensate line at
indoor unit.
Check condensate line outside to make sure it is
not obstructed.
Check condensate line to make sure it has not
been disconnected from indoor unit
Water is leaking from the outdoor unitDuring operation in high−humidity areas, conden-
sate will form on cold outdoor refrigerant pipes.
When heat pump is operating in defrost mode, ice
will thaw from around outdoor coil and water will
flow from the unit
Clicking noise heard insideSometimes, the sound of the outdoor unit fan or
compressor relay can be transmitted in a way that
makes it seem to be coming from the indoor unit
Indoor fan is not workingHeat pump units −− In HEAT mode, a timed delay
keeps indoor fan off for two minutes to prevent
unheated air from being circulated by the indoor
Heat pump units −− In HEAT mode, cold outdoor
temperatures and high humidity cause frost to ac-
cumulate on the outdoor unit. When this happens,
the unit will enter a defrost cycle. The indoor fan is
off during the 3 − 12 minute cycle.
In DEHUMIDIFICATION mode, indoor fan opera-
tion may be stopped to avoid delivery of moist air
to the room. Do not adjust temperature setting

Lennox air conditioner Error Codes

If a problem occurs with the system, an error code will replace the temperature setting displayed on
the front cover of the indoor unit. If more than one error has occurred, the codes will alternate so
that all codes are shown. Make note of the code (E4, F6, H4, etc.), then reset the display by pressing
the ON/OFF button on the wireless remote. Press the ON/OFF button a second time to reapply pow-
er to system. If code is still displayed, disconnect and restore power at the unit disconnect switch
or circuit breaker. If the problem was temporary, the code will not reappear. If the error code re−ap-
pears after power has been broken and restored at the disconnect switch or circuit breaker, call a
licensed professional service technician.