Carrier 48AK Installation, Start-up And Service Instructions Manual

Also see for 48AJ: Installation instructions Operation and service guide Started guide Operating and service guide

Contents

82The Time Guard® function maintains a minimum offtime of 5 minutes, a minimum ON time of 10 seconds, and aminimum delay before starting the second compressor of10 seconds.If the compressors have been off for more than 15 minutesand the OAT (outdoor-air temperature) is less than 45 F, thenthe safeties will be ignored for 5 minutes. At all times, safetieswill be used.Heating and cooling will be mutually locked out on demandon a first call basis. The heating and the cooling functions can-not be operating simultaneously.COOLING, VARIABLE AIR VOLUME (VAV) UNITS —On power up, the control module will activate the initializationsoftware of the control board. The initialization software thenreads DIP switch no. 1 position to determine CV or VAV oper-ation. Initialization clears all alarms and alerts, re-maps the in-put/output database for VAV operation, sets maximum heatstages to 1 and sets maximum cool stages to 6. The controlmodule reads DIP switch no. 3 and determines if the unit willuse expansion board operation. Power up takes a random timeof 1 to 63 seconds plus 5 minutes the first time power is sent tothe control board after a power outage.The control module will determine if an interface (linkage)is active and if the unit will operate in a Digital Air Volume(DAV) mode. In a DAV system, the room terminals areequipped with microprocessor controls that give commands tothe base unit module. If an interface is active, the control willreplace local comfort set points, space and return air tempera-tures and occupancy status with the linkage data supplied.The control module will determine occupancy status fromTime Schedules (if programmed), Remote Occupied/Unoccu-pied input, global occupancy, or DAV. If Temperature Com-pensated Start is active, the unit will be controlled as in theOccupied mode.NOTE: The temperature compensated start is a period of timecalculated to bring the unit on while in Unoccupied mode toreach the occupied set point when occupancy occurs.The control module will set the appropriate operating modeand fan control. The control module will turn VFD on if Occu-pied mode is evident.For units equipped with a start/stop switch only (no spacetemperature sensor), if in Unoccupied mode and valid return-air temperature reading is available (either from a sensor orDAV), the control will monitor return-air temperature againstUnoccupied Heat and Cool set points.For units with a start/stop switch and a space temperaturesensor, the control module will start the VFD whenever SPT isoutside of the set points (Unoccupied Heat or UnoccupiedCool). The VFD may also be started by nighttime thermostatvia remote Occupied/Unoccupied input or by a TemperatureCompensated Start algorithm. When VFD is running in a nor-mal mode, the control will start heating or cooling as requiredto maintain supply-air temperature at the supply air set point(SASP) plus the reset (when enabled). The reset value is deter-mined by SAT (supply-air temperature) reset and/or space tem-perature reset algorithms. The space temperature reset is onlyavailable when enabled through software.When cooling, the control will energize the power exhaustenable output to the external power exhaust controller, whenpower exhaust is used.If in Occupied mode, the control module will perform econ-omizer control (economizer control same as described abovefor CV units). If in Unoccupied mode, the control module willperform nighttime free cool and IAQ pre-occupancy purge asrequired (when enabled through software). When DX (directexpansion) cooling is called, the outdoor fans will alwaysoperate.The control will run continuous diagnostics for alarms/alerts; respond to CCN communications and perform any con-figured network POC (product outboard controls) functionssuch as time and outdoor-air temperature broadcast and globalbroadcast; and perform Fire/Smoke control if equipped withpower exhaust.GAS HEATING, CONSTANT VOLUME (CV) UNITS —The gas heat units incorporate 2 (48AJ,AK,AW,AY020-050and 48EJ,EK,EW,EY024-048) or 3 (48AJ,AK,AW,AY060 and48EJ,EK,EW,EY054-068) separate systems to provide gasheat. Each system incorporates its own induced-draft motor, In-tegrated Gas Control (IGC) board, 2 stage gas valve, manifold,etc. The systems are operated in parallel; for example, whenthere is a call for first stage heat, all induced-draft motors oper-ate, all gas valves are energized, and both IGC boards initiatespark.All of the gas heating control is performed through the IGCboards (located in the heating section). The control moduleboard serves only to initiate and terminate heating operation.The control module board is powered by 24 vac. When thethermostat or room sensor calls for heating, power is sent fromthe control module board to W on each of the IGC boards. AnLED on the IGC board will be on during normal operation. Acheck is made to ensure that the rollout switches and limitswitches are closed and the induced-draft motors are not run-ning. The induced-draft motors are then energized, and whenspeed is proven with the hall effect sensor on the motor, theignition activation period begins. The burners will ignite within5 seconds.When ignition occurs the IGC board will continue to moni-tor the condition of the rollout and limit switches, the hall effectsensor, as well as the flame sensor. If the unit is controlledthrough a room thermostat set for fan auto., 45 seconds afterignition occurs, the indoor-fan motor will be energized and theoutdoor-air dampers will open to their minimum position. If forsome reason the overtemperature limit opens prior to the startof the indoor fan blower, on the next attempt, the 45-second de-lay will be shortened to 5 seconds less than the time from initi-ation of heat to when the limit tripped. Gas will not be inter-rupted to the burners and heating will continue. Once modified,the fan on delay will not change back to 45 seconds unlesspower is reset to the control. If the unit is controlled through aroom sensor, the indoor fan will be operating in the Occupiedmode and the outdoor-air dampers will be in the minimumposition.If the unit is controlled with a room sensor in the Unoccu-pied mode, the indoor fan will be energized through the IGCboard with a 45-second delay and the outside-air dampers willmove to the IAQ position (generally set to zero in the Unoccu-pied mode). The IAQ feature is enabled through system soft-ware. If IAQ is not enabled, dampers will move to the mini-mum position.When additional heat is required, W2 closes and initiatespower to the second stage of the main gas valves. When thethermostat is satisfied, W1 and W2 open and the gas valvesclose interrupting the flow of gas to the main burners. If the callfor W1 lasted less than 1 minute, the heating cycle will not ter-minate until 1 minute after W1 became active. If the unit iscontrolled through a room thermostat set for fan auto., theindoor-fan motor will continue to operate for an additional45 seconds then stop and the outdoor-air dampers will close. Ifthe overtemperature limit opens after the indoor motor isstopped within 10 minutes of W1 becoming inactive, on thenext cycle the time will be extended by 15 seconds. The maxi-mum delay is 3 minutes. Once modified, the fan off delay willnot change back to 45 seconds unless power is reset to the con-trol. If the unit is controlled through a room sensor, the indoorfan will be operating in the Occupied mode and turned off after45 seconds in the Unoccupied mode.