Bard WH422D Installation Instructions Manual

Manual 2100-443Page 17DEFROST CYCLEThe defrost cycle is controlled by temperature and timeon the solid state heat pump control. See Figure 11.When the outdoor temperature is in the lower 40° Ftemperature range or colder, the outdoor coiltemperature is 32° F or below. This coil temperature issensed by the coil temperature sensor mounted near thebottom of the outdoor coil. Once coil temperaturereaches 30° F or below, the coil temperature sensorsends a signal to the control logic of the heat pumpcontrol and the defrost timer will start.After 60 minutes at 30° F or below, the heat pumpcontrol will place the system in the defrost mode.During the defrost mode, the refrigerant cycle switchesback to the cooling cycle, the outdoor motor stops,electric heaters are energized, and hot gas passingthrough the outdoor coil melts any accumulated frost.When the temperature rises to approximately 57° F, thecoil temperature sensor will send a signal to the heatpump control which will return the system to heatingoperations automatically.If some abnormal or temporary condition such as a highwind causes the heat pump to have a prolonged defrostcycle, the heat pump control will restore the system toheating operation automatically after 10 minutes.The heat pump defrost control board has an option of30, 60 or 90 minutes setting. All models are shippedfrom the factory on the 60 minute pin. If specialcircumstances require a change to another time, removethe wire from the 60 minute terminal and reconnect tothe desired terminal. The manufacturer'srecommendation is for 60 minute defrost cycles. Referto Figure 11There is a cycle speed up jumper on the control. Thiscan be used to reduce the time between defrost cycleoperation without waiting for time to elapse.Use a small screwdriver or other metallic object, oranother 1/4 inch QC, to short between the SPEEDUPterminals to accelerate the HPC timer and initiatedefrost.Be careful not to touch any other terminals with theinstrument used to short the SPEEDUP terminals. Itmay take up to 10 seconds with the SPEEDUPterminals shorted for the speedup to be completed andthe defrost cycle to start.As soon as the defrost cycle kicks in remove theshorting instrument from the SPEEDUP terminals.Otherwise the timing will remain accelerated and runthrough the 1 minute minimum defrost length sequencein a matter of seconds and will automatically terminatethe defrost sequence.There is an initiate defrost jumper (sen jump) 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.By placing a jumper across the SEN JMP terminals (a1/4 inch QC terminal works best) the defrost sensormounted on the outdoor coil is shunted out and willactivate the timing circuit. This permits the defrostcycle to be checked out in warmer weather conditionswithout the outdoor temperature having to fall into thedefrost region.In order to terminate the defrost test the SEN JMPjumper must be removed. If left in place too long thecompressor could stop due to the high pressure controlopening because of high pressure condition created byoperating in the cooling mode with outdoor fan off.Pressure will rise fairly fast as there is likely no actualfrost on the outdoor coil in this artificial test condition.There is also a 5 minute compressor time delay functionbuilt into the HPC. This is to protect the compressor fromshort cycling conditions. In some instances it is helpful tothe service technician to override or speed up this timingperiod, and shorting out the SPEEDUP terminals for a fewseconds can do this.FIGURE 11DEFROST CONTROL BOARD