Bard WH602, WH483, WH421 installation instructions Figure 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.

FIGURE 10

DEFROST CONTROL BOARD

Manual 2100-399 Page 16