Bard QH242 Installation instructions manual - page 26
Manual 2100-379
Page 24
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 10 minutes.
There are three settings on the heat pump control – 30
minute, 60 minute and 90 minute. Models are shipped
wired on the 30 minute setting for greatest operating
economy. If special circumstances require a change to
another time, remove wire connected to terminal 30 and
reconnect to desired terminal. Refer to Figure 21. The
manufacturer’s recommendation is for 30 minute
defrost cycles.
There is a cycle speed up jumper on the control. This
can be used to reduce the time between defrost cycle
operation without waiting for time to elapse.
There is an initial defrost jumper (sen jmp) on the
control that can be used at any outdoor ambient during
the heating cycle to simulate a 0° 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.
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 sensor mounted near the bottom of
the outdoor coil. Once coil temperature reaches 30° F
or below, the coil sends a signal to the control logic of
the heat pump control and the defrost timer will start.
After 30 minutes 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 sensor will send a signal to the heat pump control
which will return the system to heating operations
automatically.
FIGURE 21
HEAT PUMP CONTROL BOARD
MIS-973