Bard W18H2-A Installation Instructions Manual

Bard W18H2-A Installation Instructions Manual Manual pdf 17 page image

Manual 2100-604APage 17 of 28SEQUENCE OF OPERATIONCOOLING – Circuit R-Y makes at thermostat pullingin compressor contactor, starting the compressorand outdoor motor. The G (indoor motor) circuit isautomatically completed on any call for cooling operationor can be energized by manual fan switch on subbase forconstant air circulation.HEATING – A 24V solenoid coil on reversing valvecontrols heating cycle operation. Two thermostatoptions, one allowing “Auto” changeover from cycle tocycle and the other constantly energizing solenoid coilduring heating season, and thus eliminating pressureequalization noise except during defrost, are to be used.On “Auto” option a circuit is completed from R-W1 andR-Y on each heating “on” cycle, energizing reversingvalve solenoid and pulling in compressor contactorstarting compressor and outdoor motor. R-G also makestarting indoor blower motor. Heat pump heating cyclenow in operation. The second option has no “Auto”changeover position, but instead energizes the reversingvalve solenoid constantly whenever the system switch onsubbase is placed in “Heat” position, the “B” terminalbeing constantly energized from R. A Thermostat demandfor heat completes R-Y circuit, pulling in compressorcontactor starting compressor and outdoor motor. R-Galso make starting indoor blower motor.PRESSURE SERVICE PORTSHigh and low pressure service ports are installed onall units so that the system operating pressures can beobserved. Pressure tables can be found later in themanual covering all models. It is imperative to matchthe correct pressure table to the unit by model number.See Tables 3A and 3B.DEFROST CYCLEThe defrost cycle is controlled by temperature and timeon the solid state heat pump control.When the outdoor temperature is in the lower40°F temperature range or colder, the outdoor coiltemperature is 32°F or below. This coil temperatureis sensed by the coil temperature sensor mounted nearthe bottom 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 accumulatingrun time.After 30, 60 or 90 minutes of heat pump operation at30°F or below, the heat pump control will place thesystem 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 ahigh wind causes the heat pump to have a prolongeddefrost cycle, the heat pump control will restore thesystem to heating operation automatically after 8minutes.The heat pump defrost control board has an option of30, 60 or 90-minute setting. By default, this unit isshipped from the factory with the defrost time on the60 minute pin. If circumstances require a changeto another time, remove the wire from the 60-minuteterminal and reconnect to the desired terminal. Referto Figure 8.There is a cycle speed up jumper on the control. Thiscan be used for testing purposes to reduce the timebetween defrost cycle operation without waiting fortime to elapse.Use a small screwdriver or other metallic object,or another ¼" 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.It may 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 andrun through the 1-minute minimum defrost lengthsequence in a matter of seconds and will automaticallyterminate the 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 (a¼" QC terminal works best) the defrost sensor mountedon the outdoor coil is shunted out and will activatethe timing circuit. This permits the defrost cycle tobe checked out in warmer weather conditions withoutthe outdoor temperature having to fall into the defrostregion.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 createdby operating in the cooling mode with outdoor fan off.