Carrier 48FK, JK034-074, 50FK specifications Safety Considerations, General

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/RESISTOR FAILURE

·CODE 81: RESET THERMISTOR OR POTENTIOMETER FAILURE

·CODE 82: LEAVING-AIR TEMPERATURE SET POINT POTENTIOMETER FAILURE

·CODE 83: ECONOMIZER FEEDBACK POTENTIOMETER FAILURE

·CODE 84: RESET LIMIT POTENTIOMETER FAILURE

·CODE 85: DEMAND LIMIT POTENTIOMETER (P4) FAILURE

·CODE 86: MINIMUM POSITION ECONOMIZER POTENTIOMETER FAILURE

·CODE 87: WARM-UP TEMPERATURE SET POINT

FAILURE

Thermistor Troubleshooting . . . . . . . . . . . . . . . . . . . . 47 Electronic Controls Checkout . . . . . . . . . . . . . . . . . . 47

·PROCESSOR BOARD CHECKOUT

·RELAY BOARD TROUBLESHOOTING

·DISPLAY BOARD CHECKOUT

·ACCESSORY BOARD CHECKOUT

·TWO-STEP DEMAND LIMIT CONTROL MODULE

(DLCM) TROUBLESHOOTING

Enthalpy Sensor Checkout . . . . . . . . . . . . . . . . . . . . . 51

Economizer Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Variable Frequency Drive . . . . . . . . . . . . . . . . . . . . . . 52

·STANDARD TRANSDUCER CONTROL

·EXTERNAL SIGNAL CONTROL

·SUPPLY FAN MOTOR OVERLOAD PROTECTION

VFD Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

VFD Operational Status . . . . . . . . . . . . . . . . . . . . . . . . 54

Restoring Factory VFD Defaults . . . . . . . . . . . . . . . . 54

Unit Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

START-UP CHECKLIST . . . . . . . . . . . . . . . . . . CL-1, CL-2

SAFETY CONSIDERATIONS

Installing, starting up, and servicing this equipment can be hazardous due to system pressures, electrical compo- nents; and equipment location (roof, elevated structures, etc.). Only trained, quali®ed installers and service mechanics should install, start up, and service this equipment.

When working on this equipment, observe precautions in the literature; on tags, stickers, and labels attached to the equip- ment, and any other safety precautions that apply. Follow all safety codes. Wear safety glasses and work gloves. Use care in 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 installation and service. There may be more than one disconnect switch. Tag all disconnect locations to alert others not to restore power until work is completed.

This unit uses a microprocessor-based electronic con- trol system. Do not use jumpers or other tools to short out components, or to bypass or otherwise depart from recommended procedures. Any short-to-ground of the control board or accompanying wiring may destroy the electronic modules or electrical components.

GENERAL

IMPORTANT: This literature contains controls, operation, and troubleshooting data for 48FK,JK and 50FK,FY,JK,JY variable air volume rooftop units. Use this guide in conjunction with the separate Installation Instructions literature packaged with the unit.

Carrier 48FK,JK and 50FK,FY,JK,JY units provide ven- tilation, cooling, and heating (when equipped) in Variable Air Volume (VAV) applications. These units contain factory- installed controls which provide full system management. The unit controls also perform self diagnostic tests at unit start-up, monitor operation of the unit, and provide alarms. Information on system operation and status are sent to the central processors by various sensors that are located at the unit and in the conditioned space. Each unit is equipped with a display board.

Rooftop Information Ð The rooftop controls cycle supply-fan motor, compressors, and unloaders to maintain the proper temperature conditions. The controls also cycle condenser fans to maintain suitable head pressure. Safeties are 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 checked for proper operation.

IMPORTANT: The ®eld-supplied and installed switch (or timeclock) MUST BE CLOSED to put unit into the Occupied mode. Unit WILL NOT START until this is accomplished. See base unit installation instructions literature for details.

VAV Control System Ð The 30 to 100-ton VAV roof- top units contain a microprocessor-based electronic control system 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 Ð The processor board, shown in Fig. 1, contains the logic and the necessary hardware to drive the outputs and the display board. The processor board is enclosed by a sheet metal cover and a heater. The heater is controlled by a thermostat to keep the processor temperature above 32 F (0° C). All electrical connections are made to the processor board through wire and ribbon cables.

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