York DC SERIES Installation Manual

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York DC SERIES Installation Manual Manual pdf 28 page image

5120410-XIM-B-021628 Johnson Controls Unitary ProductsAutoThe control determines the type of free cooling changeoverbased on which sensors are present and reliable. Conditionsinclude:• Return and outside air dry bulb = dry bulb changeover• Return and outside air dry bulb and outside air humidity =single enthalpy• Return and outside air dry bulb and return and outside airhumidity = dual enthalpy• If either the return or outside air dry bulb sensors areunreliable, free cooling is not availableFree Cooling OperationWhen the control determines that the outside air is suitable, thefirst stage of cooling will always be free cooling.ThermostatIn free cooling, with a thermostat input to Y1, the dampersmodulate to control the supply air temperature to theEconomizer Setpoint +/- 1°F (default 55°F).If the thermostat provides an input to Y2 and the parameterCompressors Off in Free Cooling is turned OFF a compressoroutput energizes. The economizer dampers continue tomodulate to control the supply air temperature to theEconomizer Setpoint.If the supply air temperature cannot be maintained within 5°F ofthe economizer setpoint, the first stage compressor (C1) will beturned on. Second stage compressor (C2) will be added asneeded to keep the supply air temperature within the 5°F of theeconomizer setpoint.SensorIn free cooling, with a demand from the zone/return sensor forthe first stage of cooling, the dampers modulate to control thesupply air temperature to the Economizer Setpoint +/- 1°F.If the economizer output is at 100% and the SAT is greater thanthe Economizer setpoint + 1°F, the control starts a 12-minutetimer to energize a compressor output.If at any time the economizer output drops below 100% thetimer stops and resets when the economizer output returns to100%.Once a compressor output is turned ON, the economizerdampers continue to modulate to control the supply airtemperature to the Economizer Setpoint.At no time will a compressor output be turned ON if theeconomizer output is less than 100%, even if the differentialbetween zone (or return) temperature and the current coolingsetpoint is great enough to demand more than one stage ofcooling.If the economizer output goes to minimum position and the SATis less than Economizer Setpoint -1°F, the control starts a 12-minute timer to de-energize a compressor output.If at any time the economizer output goes above the minimumposition the timer stops and resets when the economizer outputreturns to minimum position.If the demand for cooling from the space/return is satisfied, theeconomizer output will modulate to minimum position and thecompressor outputs will be de-energized as long as theirminimum run timers have expired.Power ExhaustSetpointsa. Economizer Enable ONb. Power Exhaust Enable ONc. Modulating Power Exhaust OFFd. Exhaust VFD Installed OFFe. Building Pressure Sensor Enabled OFFf. Econo Damper Position For Exh Fan ON Percentg. Econo Damper Position For Exh Fan OFF PercentInputsNo inputs are present for non-modulating power exhaust.Outputsa. 2-10 VDC from ECON on Economizer Expansion moduleb. 24 VAC from EX-FAN to energize exhaust fan onEconomizer Expansion moduleOperationOperation details include:a. Compares economizer output to the Economizer DamperPosition For Exhaust Fan On and OFF.b. Energizes exhaust fan when economizer output is aboveEconomizer Damper Position For Exhaust Fan On.c. De-energizes exhaust fan when economizer output isbelow the Economizer Damper Position for Exhaust FanOFF