Defrost Cycle; Low Pressure Switch Bypass Operation - Bard W24HY-A Installation Instructions Manual

thermostat. This will increase the humidity removal
up to 35% and provide a much more comfortable
environment.
NOTE: Units with mechanical dehumidification
require an additional connection to be made
when enabling Balanced Climate. Refer to
dehumidification supplemental instructions for
this step.
This mode will also increase the supply temperature
when in heating mode. When Balanced Climate mode
is activated it is employed in both heating and cooling
modes.
If the application is likely to require air conditioning
operation below 60°F outdoor conditions, a low
ambient control (LAC) kit must be installed. The LAC
kit is equipped with an outdoor temperature switch
that disables Balanced Climate mode when the outdoor
temperature drops below 50°F. This prevents potential
evaporator coil freeze up issues. The LAC kit also comes
with an evaporator freeze protection thermostat that cuts
out the compressor if the evaporator begins to freeze up.
If the unit is being installed with any ventilation
package, a Bard LAC kit must be installed. Failure
to utilize an LAC with any heat pump can cause coil
freeze up.
Balanced Climate can readily be applied to duct-free
(supply and return air grille) applications. It may also
be applied to ducted applications with limited static
of 0.20" ESP (total including both supply and return
statics). Consult Bard Application Engineering for
details prior to implementation.
CAUTION: Balanced Climate is not a replacement for
a dehumidification (hot gas reheat) unit for extreme
applications, but rather an enhancement feature for
limited climates and applications.

Defrost Cycle

The defrost cycle is controlled by temperature and time
on the solid state heat pump control.
When the outdoor temperature is in the lower
40°F temperature range or colder, the outdoor coil
temperature is 32°F or below. This coil temperature is
sensed by the coil temperature sensor mounted near
the bottom of the outdoor coil. Once coil temperature
reaches 30°F or below, the coil temperature sensor
sends a signal to the control logic of the heat pump
control and the defrost timer will start accumulating
run time.
After 30, 60 or 90 minutes of heat pump operation at
30°F or below, the heat pump control will place the
system in the defrost mode.
During the defrost mode, the refrigerant cycle switches
back to the cooling cycle, the outdoor motor stops,
electric heaters are energized and hot gas passing
through the outdoor coil melts any accumulated frost.
When the temperature rises to approximately 57°F, the
coil temperature sensor will send a signal to the heat
pump control which will return the system to heating
operations automatically.
If some abnormal or temporary condition such as a high
wind causes the heat pump to have a prolonged defrost
cycle, the heat pump control will restore the system to
heating operation automatically after 8 minutes.
The heat pump defrost control board has an option of
30-, 60- or 90-minute setting. By default, this unit
is shipped from the factory with the defrost time on
the 60-minute pin. If circumstances require a change
to another time, remove the wire from the 60-minute
terminal and reconnect to the desired terminal. Refer
to Figure 10 on page 31.
There is a cycle speed up jumper on the control. This
can be used for testing purposes to reduce the time
between defrost cycle operation without waiting for
time to elapse.
Use a small screwdriver or other metallic object, or
another 1/4" QC, to short between the SPEEDUP
terminals to accelerate the HPC timer and initiate
defrost.
Be careful not to touch any other terminals with the
instrument used to short the SPEEDUP terminals.
It may take up to 10 seconds with the SPEEDUP
terminals shorted for the speedup to be completed and
the defrost cycle to start.
As soon as the defrost cycle kicks in, remove the
shorting instrument from the SPEEDUP terminals.
Otherwise the timing will remain accelerated and
run through the 1-minute minimum defrost length
sequence in a matter of seconds and will automatically
terminate the defrost sequence.
There is an initiate defrost jumper (sen jump) on the
control that can be used at any outdoor ambient during
the heating cycle to simulate a 0°F coil temperature.
This can be used to check defrost operation of the unit
without waiting for the outdoor ambient to fall into the
defrost region.
By placing a jumper across the SEN JMP terminals (a
1/4" QC terminal works best) the defrost sensor mounted
on the outdoor coil is shunted out and will activate
the timing circuit. This permits the defrost cycle to be
checked out in warmer weather conditions without the
outdoor temperature having to fall into the defrost region.
In order to terminate the defrost test, the SEN JMP
jumper must be removed. If left in place too long, the
compressor could stop due to the high pressure control
opening because of high pressure condition created
by operating in the cooling mode with outdoor fan off.
Pressure will rise fairly fast as there is likely no actual
frost on the outdoor coil in this artificial test condition.
Manual 2100-790
Page 29 of 49