Bard WALL MOUNTED PACKAGE HEAT PUMPS WH602 - Manual (Page 18)

Manual 2100-399
Page 16
FIGURE 10
DEFROST CONTROL BOARD
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 10-minute maximum defrost length
sequence in a matter of seconds and will automatically
terminate the defrost sequence.
There is an initial defrost (SEN JMP) jumper 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.
The jumper connection (SEN JMP) on the heat Pump
Control (HPC) that can be used during the heating cycle
to simulate a 0 degree coil condition and initiate the
defrost sequence. By placing a jumper across the
SEN JMP terminals (1/4 inch 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.
There are three time settings on the HPC — 30, 60 or
on minutes. These are elapsed run-time values, and the
outdoor coil temperature sensor must be below the 30
degree equivalent resistance value for the timer to
accumulate time towards the actual defrost cycle event.
Using the SEN JMP terminals will force the timer to
run continuously.
The next event is the actual defrost cycle when the
reversing valve shifts the refrigerant system back to the
cooling mode, and the outdoor fan motor is turned off
to speed the heating of the outdoor coil and melting of
any accumulated frost. The SPEEDUP terminals can be
used to reduce the 30,60 or 90 minute real-time periods
to a matter of seconds. Electric heat is typically turned
on to temper the supply air temperature being delivered
into the building during the defrost cycle.
There is also a 5-minute compressor time delay
function built into the HPC. This is to protect the
compressor from short cycling conditions. In some
instances it is helpful to the service technician to
override or speedup this timing period, and shorting out
the SPEEDUP terminals for a few seconds can do this.