York ZR Series Installation Manual

Also see for ZR SERIES: Technical guide Wiring diagrams Installation manual

Contents

275864-YIM-F-0213Johnson Controls Unitary Products 43controlled. On any fault, only the associated system will beaffected by any safety/preventive action. The other refrigerantsystem will continue in operation unless it is affected by thefault as well.The unit control board monitors the temperature limit switch ofelectric heat units and the temperature limit switch and the gasvalve of gas furnace units.Compressor ProtectionIn addition to the external pressure switches, the compressorsalso have inherent (internal) protection. If there is an abnormaltemperature rise in a compressor, the protector will open toshut down the compressor. The UCB incorporates features tominimize compressor wear and damage. An Anti-Short CycleDelay (ASCD) is utilized to prevent operation of a compressortoo soon after its previous run. Additionally, a minimum runtime is imposed any time a compressor is energized.The ASCD is initiated on unit start-up and on any compressorreset or lock-out.Flash CodesThe UCB will initiate a flash code associated with errors withinthe system. Refer to UNIT CONTROL BOARD FLASH CODESTable 26.ResetRemove the call for cooling, by raising thermostat setting higherthan the conditioned space temperature. This resets anypressure or freezestat flash codes.Reheat Mode Sequence Of OperationThe reheat control board allows the user to select two differentmodes of operation via a jumper connection on the board. (SeeReheat Control Board.) Each mode is described below. Refer toReheat Controls - Part 1 and Part 2 when reading this section.“Normal” ModeWhen the reheat control board (RCB) detects a need fordehumidification (24VAC) at "HUM" via the field supplieddehumidistat connected to RHTB-1 and RHTB-2 and there isnot a call for cooling, it energizes the hot gas relay (HGR),which energizes the 3-way valve (SOL 3), the condenser coilvalve (SOL 2), and de-energizes the reheat coil bleed valve(SOL 1). The Y1 signal is passed to the unit control board(UCB), which engages circuit # 1, resulting in circuit #1 reheatmode operation.When the room thermostat calls for first stage cooling, with orwithout a call for dehumidification, the RCB senses a signalthrough "Y1", de-energizing the HGR, which de-energizes SOL3 and SOL 2, and energizes SOL 1, engaging circuit # 1,resulting in circuit #1 cooling mode operation.When the room thermostat calls for second stage cooling, theRCB senses a signal through "Y1" & "Y2" and engages circuit#1 and circuit #2 in the cooling mode.Indoor blower operation is initiated upon a call for first stagecooling, second stage cooling or dehumidification.Anytime there is a call for 2 stages of cooling, the unit will notoperate in the reheat mode, even if there is a call fordehumidification at "HUM".The unit will not operate in the reheat mode if there is any callfor heating.On units with economizers, the unit will not operate in thereheat mode if there is a call for cooling and the economizer isoperating as first stage of cooling.All safety devices function as previously described."Alternate” ModeWhen the RCB detects a need for dehumidification (24VAC) at"HUM" via the field supplied dehumidistat connected to RHTB-1and RHTB-2, and there is not a call for cooling, it energizes theHGR, which energizes the SOL 3, SOL 2, and de-energizesSOL 1. The unit then operates with circuit #1 in reheat modeand circuit #2 in cooling mode.When the room thermostat calls for first stage cooling while thereis still a call for dehumidification, no operational change is made.The call for cooling is ignored and the unit continues to operatewith circuit #1 in reheat mode and circuit #2 in cooling mode.When the room thermostat calls for second stage cooling, theRCB senses a signal through "Y1" & "Y2" and de-energizes theHGR, which de-energizes SOL 3 and SOL 2, and energizesSOL 1. Both circuits operate in the cooling mode.Indoor blower operation is initiated upon a call for first stagecooling, second stage cooling or dehumidification.Anytime there is a call for 2 stages of cooling, the unit will notoperate in the reheat mode, even if there is still a call fordehumidification at "HUM".The unit will not operate in the reheat mode if there is any callfor heating.All safety devices function as previously described.