Carrier 48FK Controls Operation And Troubleshooting

Carrier 48FK Controls Operation And Troubleshooting Manual pdf 2 page image

CONTENTS (cont)Page• CODES 59 AND 60: LOW-PRESSURE SWITCH• CODES 63 AND 64: OIL PRESSURE SWITCH• CODE 70: ILLEGAL UNIT CONFIGURATION• CODES 71 TO 76: THERMISTOR/RESISTORFAILURE• CODE 81: RESET THERMISTOR ORPOTENTIOMETER FAILURE• CODE 82: LEAVING-AIR TEMPERATURE SET POINTPOTENTIOMETER FAILURE• CODE 83: ECONOMIZER FEEDBACKPOTENTIOMETER FAILURE• CODE 84: RESET LIMIT POTENTIOMETERFAILURE• CODE 85: DEMAND LIMIT POTENTIOMETER (P4)FAILURE• CODE 86: MINIMUM POSITION ECONOMIZERPOTENTIOMETER FAILURE• CODE 87: WARM-UP TEMPERATURE SET POINTFAILUREThermistor Troubleshooting . . . . . . . . . . . . . . . . . . . . 47Electronic Controls Checkout . . . . . . . . . . . . . . . . . . 47• PROCESSOR BOARD CHECKOUT• RELAY BOARD TROUBLESHOOTING• DISPLAY BOARD CHECKOUT• ACCESSORY BOARD CHECKOUT• TWO-STEP DEMAND LIMIT CONTROL MODULE(DLCM) TROUBLESHOOTINGEnthalpy Sensor Checkout . . . . . . . . . . . . . . . . . . . . . 51Economizer Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Variable Frequency Drive . . . . . . . . . . . . . . . . . . . . . . 52• STANDARD TRANSDUCER CONTROL• EXTERNAL SIGNAL CONTROL• SUPPLY FAN MOTOR OVERLOAD PROTECTIONVFD Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54VFD Operational Status . . . . . . . . . . . . . . . . . . . . . . . . 54Restoring Factory VFD Defaults . . . . . . . . . . . . . . . . 54Unit Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54START-UP CHECKLIST . . . . . . . . . . . . . . . . . . CL-1, CL-2SAFETY CONSIDERATIONSInstalling, starting up, and servicing this equipment canbe hazardous due to system pressures, electrical compo-nents; and equipment location (roof, elevated structures, etc.).Only trained, qualified installers and service mechanics shouldinstall, start up, and service this equipment.When working on this equipment, observe precautions inthe literature; on tags, stickers, and labels attached to the equip-ment, and any other safety precautions that apply. Follow allsafety codes. Wear safety glasses and work gloves. Use carein handling, rigging, and setting this equipment, and in han-dling all electrical components.Electrical shock can cause personal injury and death.Shut off all power to this equipment during installationand service. There may be more than one disconnectswitch. Tag all disconnect locations to alert others notto restore power until work is completed.This unit uses a microprocessor-based electronic con-trol system. Do not use jumpers or other tools to shortout components, or to bypass or otherwise depart fromrecommended procedures. Any short-to-ground of thecontrol board or accompanying wiring may destroy theelectronic modules or electrical components.GENERALIMPORTANT: This literature contains controls,operation, and troubleshooting data for 48FK,JK and50FK,FY,JK,JY variable air volume rooftop units. Usethis guide in conjunction with the separate InstallationInstructions literature packaged with the unit.Carrier 48FK,JK and 50FK,FY,JK,JY units provide ven-tilation, cooling, and heating (when equipped) in VariableAir Volume (VAV) applications. These units contain factory-installed controls which provide full system management.The unit controls also perform self diagnostic tests at unitstart-up, monitor operation of the unit, and provide alarms.Information on system operation and status are sent to thecentral processors by various sensors that are located at theunit and in the conditioned space. Each unit is equipped witha display board.Rooftop Information — The rooftop controls cyclesupply-fan motor, compressors, and unloaders to maintainthe proper temperature conditions. The controls also cyclecondenser fans to maintain suitable head pressure. Safetiesare continuously monitored to prevent the unit from oper-ating under abnormal conditions. The controls provide con-trol of economizer and cycle or control heating as required.The controls also allow the service person to operate a‘quick test’so that all the controlled components can be checkedfor proper operation.IMPORTANT: The field-supplied and installed switch(or timeclock) MUST BE CLOSED to put unit intothe Occupied mode. Unit WILL NOT START until thisis accomplished. See base unit installation instructionsliterature for details.VAV Control System — The 30 to 100-ton VAV roof-top units contain a microprocessor-based electronic controlsystem that controls and monitors the rooftop unit functions.The VAV control system is composed of several components:• processor board• relay board• display board• thermistors• compressor operation feedback (control relay)• accessory board• temperature reset package*• single-step demand limit*• two-step demand limit control module**Field-installed accessories.The VAV control system monitors and controls the fol-lowing functions of the rooftop unit:• supply-air temperature (unit capacity)• morning warm-up or electric heat (if equipped)• head pressure control, fan cycling• economizer position• diagnostic display• unit check-out (quick test)• supply air temperature reset (if equipped)• demand limiting (if equipped)Processor Board — The processor board, shown inFig. 1, contains the logic and the necessary hardware to drivethe outputs and the display board. The processor board isenclosed by a sheet metal cover and a heater. The heater iscontrolled by a thermostat to keep the processor temperatureabove 32 F (0° C). All electrical connections are made to theprocessor board through wire and ribbon cables.2