Bard WH421 Installation Instructions Manual

Also see for WH421: Specifications Installation instructions

Manual 2100-399Page 16FIGURE 10DEFROST CONTROL BOARDAs soon as the defrost cycle kicks in, remove theshorting instrument from the SPEEDUP terminals.Otherwise the timing will remain accelerated and runthrough the 10-minute maximum defrost lengthsequence in a matter of seconds and will automaticallyterminate the defrost sequence.There is an initial defrost (SEN JMP) jumper on thecontrol that can be used at any outdoor ambient duringthe heating cycle to simulate a 0° coil temperature.This can be used to check defrost operation of the unitwithout waiting for the outdoor ambient to fall into thedefrost region.The jumper connection (SEN JMP) on the heat PumpControl (HPC) that can be used during the heating cycleto simulate a 0 degree coil condition and initiate thedefrost sequence. By placing a jumper across theSEN JMP terminals (1/4 inch QC terminal works best)the defrost sensor mounted on the outdoor coil isshunted out and will activate the timing circuit. Thispermits the defrost cycle to be checked out in warmerweather conditions without the outdoor temperaturehaving to fall into the defrost region.There are three time settings on the HPC — 30, 60 oron minutes. These are elapsed run-time values, and theoutdoor coil temperature sensor must be below the 30degree equivalent resistance value for the timer toaccumulate time towards the actual defrost cycle event.Using the SEN JMP terminals will force the timer torun continuously.The next event is the actual defrost cycle when thereversing valve shifts the refrigerant system back to thecooling mode, and the outdoor fan motor is turned offto speed the heating of the outdoor coil and melting ofany accumulated frost. The SPEEDUP terminals can beused to reduce the 30,60 or 90 minute real-time periodsto a matter of seconds. Electric heat is typically turnedon to temper the supply air temperature being deliveredinto the building during the defrost cycle.There is also a 5-minute compressor time delayfunction built into the HPC. This is to protect thecompressor from short cycling conditions. In someinstances it is helpful to the service technician tooverride or speedup this timing period, and shorting outthe SPEEDUP terminals for a few seconds can do this.