Page 26
505328M 06/09
DETAILED DEFROST MODE OPERATION
The defrost mode has three basic operational modes
which are defrost cycles, actuation and termination. These
modes are described as follows:
Defrost Cycles
The demand DCB initiates a defrost
cycle based on either
frost detection
or
time
.
Event
Description
Frost
Detection
If the compressor runs longer than 30
minutes and the actual difference between
the clear coil and frosted coil temperatures
exceeds the maximum difference allowed
by the DCB, a defrost cycle will be initiated.
IMPORTANT − The DCB will allow a
greater accumulation of frost and will
initiate fewer defrost cycles than a
time/temperature defrost system.
Time
If six hours of heating mode compressor
run time has elapsed since the last defrost
cycle while the coil temperature remains
below 35°F (2°C), the DCB will initiate a
defrost cycle.
Actuation
When the reversing valve is de−energized,
the Y1 circuit is energized, and the coil temperature is
below 35°F (2°C), the DCB logs the compressor run time.
If the DCB is not calibrated, a defrost cycle will be initiated
after 30 minutes of heating mode compressor run time.
The DCB will attempt to self−calibrate after this (and all
other) defrost cycle(s).
Calibration success depends on stable system
temperatures during the 20−minute calibration period. If
the DCB fails to calibrate, another defrost cycle will be
initiated after 45 minutes of heating mode compressor run
time. Once the DCB is calibrated, it initiates a demand
defrost cycle when the difference between the clear coil
and frosted coil temperatures exceeds the maximum
difference allowed by the DCB or after six hours of heating
mode compressor run time has been logged since the last
defrost cycle.
NOTE − If ambient or coil fault is detected, the DCB will not
execute the TEST mode.
Termination
The defrost cycle ends when the coil
temperature exceeds the termination temperature or after
14 minutes of defrost operation. If the defrost is terminated
by the 14−minute timer, another defrost cycle will be
initiated after 30 minutes of run time.
DCB DIAGNOSTICS
See table 16 on page 24 to determine DCB operational
conditions and to diagnose cause and solution to
problems.
Maintenance
Before the start of each heating and cooling season, the
following service checks should be performed by a
qualified service technician. First, turn off electrical power
to the unit prior to performing unit maintenance.
WARNING
Electric shock hazard.
Can cause injury or death.
Before attempting to perform any
service or maintenance, turn the
electrical power to unit OFF at
disconnect switch(es). Unit may have
multiple power supplies.
S
Inspect and clean the outdoor and indoor coils. The
outdoor coil may be flushed with a water hose.
NOTE − It may be necessary to flush the outdoor coil
more frequently if it is exposed to substances which
are corrosive or which block airflow across the coil
(e.g., pet urine, cottonwood seeds, etc.)
S
Visually inspect the refrigerant lines and coils for leaks.
S
Check wiring for loose connections.
S
Check voltage at the indoor and outdoor units (with
units operating).
S
Check the amperage draw at the outdoor fan motor,
compressor, and indoor blower motor. Values should
be compared with those given on unit nameplate.
S
Check, clean (or replace) indoor unit filters.
S
Check the refrigerant charge and gauge the system
pressures.
S
Check the condensate drain line for free and
unobstructed flow; clean, if necessary.
S
Outdoor unit fan motor is prelubricated and sealed. No
further lubrication is needed.
NOTE − If owner reports insufficient cooling, the unit
should be gauged and refrigerant charge checked.
Refer to section on refrigerant charging in this
instruction.
Homeowner Information
In order to ensure peak performance, your system must be
properly maintained. Clogged filters and blocked airflow
prevent your unit from operating at its most efficient level.
1.
Air Filter
Ask your Lennox dealer to show you where
your indoor unit’s filter is located. It will be either at the
indoor unit (installed internal or external to the cabinet)
or behind a return air grille in the wall or ceiling. Check
the filter monthly and clean or replace it as needed.
2.
Disposable Filter
Disposable filters should be
replaced with a filter of the same type and size.
NOTE − If you are unsure about the filter required for
your system, call your Lennox dealer for assistance.
IMPORTANT
Turn off electrical power to the unit at the
disconnect switch before performing any
maintenance. The unit may have multiple power
supplies.
3.
Reusable Filter
Many indoor units are equipped
with reusable foam filters. Clean foam filters with a
