Carrier PC 111 Operating And Troubleshooting Manual

Also see for 48FK034: Controls operation and troubleshooting

20OCCUPIED/UNOCCUPIED — The unit control system willinitiate normal occupied mode functions (including MorningWarm-up, Economizer Minimum Position, and Cooling Cycle)whenever a contact closure is made that emulates the normaltimeclock contacts. See Fig. 23. (‘‘Occupied/UnoccupiedSwitch’’). The contact closure from the BMS must be an iso-lated contact set, normally open, and suitable for 24 volts ACpilot duty.NIGHT SETBACK CONTROL — Night setback control isused to control the space to a set point level that is typicallylower than during normal occupied periods (Heating Onlymode). Some applications also require a limitation on the max-imum space temperature during unoccupied periods (Coolingmode). Both modes are possible by closing the same contactsused in the Occupied/Unoccupied control, or by installing adedicated contact set in parallel with the Occupied/ Unoccu-pied control contacts, and using the BMS space temperaturesensing system and its logic to determine when to initiate unitoperation.Once the unit operation has been initiated by the BMS con-tact closure, the unit operates in its normal occupied modemanner, initiating morning warm-up if needed (as sensed by re-turn air temperature to the unit) or cooling (controlling to cur-rent SASP value). The Night Setback Control contacts will in-terrupt normal unit operation when the BMS senses that spacetemperatures have returned to unoccupied set point levels, andthe unit will shut down normally.The contact closure from the BMS must be an isolated con-tact set, normally open, suitable for 24 volts AC pilot duty.NOTE: If the rooftop unit is equipped with a VFD and nightsetback cooling operation is intended, the fan system must becontrolled to permit FULL SUPPLY FAN AIR DELIVERYduring unoccupied cooling operation. This is most conve-niently attained by replicating the HIR relay function of therooftop unit. An HIR control sequence will force all room ter-minals to their minimum heating CFM position, thus assuringadequate airflow through the rooftop unit during night setbackcooling operation. During night setback cooling operation, thereturn-air temperature (RAT) will be well above normal levels.The higher RAT means that the air temperature leaving theevaporator coil will also be well above normal levels. This sit-uation is interpreted by the unit control system as a demand foradditional cooling stages. The unit control responds to thisdemand by bringing on more stages, until typically all stagesare active. If the VFD is not working in-step with the refrigera-tion system demand, it is possible to produce low suction pres-sures and local frosting on the evaporator coil during the nightsetback cooling operation.UNIT SUPPLY AIR SET POINT ADJUSTMENT — Theminimum Supply Air Set Point (SASP) temperature is estab-lished by the setting at Potentiometer P1 on the unit displayboard (see Fig. 6). The control point can also be adjustedupward by emulating the function of the accessory Space Tem-perature Reset package. The BMS can be used to cause thisreset by adjusting the resistance value in a variable resistancetransducer with a 4 to 20 mA or 2 to 10 vdc signal generatedby the BMS.This emulation requires the following field-supplied parts:• Variable resistance transducer (Kele RES-1 or equiva-lent, range 0 to 1000 ohms)• Series resistance with potentiometer, suitable for manualadjustment to 12.5 to 13.0 k-ohms total resistanceField Connections (see Fig. 30) — Connect fixed resistancewith manual potentiometer and variable resistance transducerin series.Connect wiring to rooftop unit at:Size 034-044: TB3-12 and TB3-15Size 054-104: TB4-12 and TB4-15Configuration — Configure as follows:1. Set DIP switch no. 2 to ON.2. Adjust manual potentiometer to 12.6 to 12.8 k-ohm.3. Configure transducer for job site input signal from BMS.4. Adjust Potentiometer (P3) on the rooftop to MAXIMUMSASP value (typically 65 to 70 F). The maximum P3 SASPcontrol limit is 70 F.Operation — Unit will initiate SASP Reset (adjust configuredSASP upward) when the sum of the resistance (fixed resistance+ potentiometer + transducer) exceeds 13.1 k-ohm. Once resetis initiated, full range of reset (P3 setting minus configuredSASP) will be reached with 500-ohm increase in transducer re-sistance (TR).During Reset mode operation, Code 21 will appear on unitdisplay board.Formula:MSP = SASP +MSP: Modified SASP (SASP plus Reset)TR: Resistance at transducerR@13.1: TR required to reach 13.1 k-ohm start levelDEMAND LIMIT (1-STAGE OR 2-STAGE) — Both of theDemand Limit functions on the units rely on external switchesto initiate the reset functions. Contact closures by the BMS canbe used in place of these switches. Contacts must be isolatedand suitable for 115-vac pilot duty operation.For Single-Step Demand Limit, emulate function of switchSW with contact closure controlled by the BMS. Set potenti-ometer P4 manually at the unit control box. Alternatively, po-tentiometer P4 might also be emulated by a variable resistancetransducer, with the BMS now able to adjust the amount of de-mand limit.For 2-Step Demand Limit, install the accessory DemandLimit Control Module (DLCM) according the instructions onpage 18. Replace switch functions Switch 1 and Switch 2 withcontact closures controlled by the BMS (see Fig. 29).Follow unit control configuration instructions in the De-mand Limit section on page 18.SUPPLY DUCT PRESSURE SET POINT ADJUSTMENT— Supply duct pressure set point adjustment from a remoteBMS is possible when the unit has been equipped with a fac-tory-option VFD (variable frequency drive). There are twomethods available:• Direct 4 to 20 mA signal• DDC direct to the VFDDirect 4 to 20 mA Signal — During normal unit operation,the factory-installed VFD receives a 4 to 20 mA signal fromthe Duct Pressure (DP) transducer which indicates current sup-ply duct pressure. The VFD then determines the appropriatefan speed (using its internal PID logic feature) and adjusts itsoutput to the supply fan motor to suit. It is possible to emulatethis 4 to 20 mA control signal by the BMS, which will transfercontrol of the VFD to the BMS.NOTE: When providing a direct 4 to 20 mA signal to the VFDfrom a BMS with DP logic, disable the PID (proportion inte-grated derivative calculation process) feature of the VFD.DDC Direct to the VFD — Several accessory interfaceboards are available for the VFDs that permit direct communi-cation between the VFD and several BMS communication sys-tems. Contact your Carrier representative for information onselecting an appropriate accessory interface board and thename of the local service office (for sale and installation of theaccessory boards).[ (P3 — SASP) X (0.6 F) X (TR — R@13.3) ](3) (100 ohm)