Carrier 48/50HC04-28 Controls, Start-up, Operation And Troubleshooting

Also see for 50HCQ04---12: Controls, Start-Up, Operation and Troubleshooting Instructions Service and maintenance instructions

Carrier 48/50HC04-28 Controls, Start-up, Operation And Troubleshooting Manual pdf 25 page image

25Fan StatusFan Status may be configured on any unused binary inputchannel. A typical application would be an airflow switch,current sensing relay, or other device that provides a supplyfan running verification. Enabling this function displays thesupply fan’s status on the equipment graphic. If thecontroller loses fan status during operation, heating andcooling are disabled, the economizer damper (if available) isclosed, and an alarm for loss of status is indicated. If the fanstatus is on when the controller is commanding the fan off,the unit remains in the off state. An alarm is generatedindicating that the fan is running when it should be off.Filter StatusFilter status may be configured on any unused binary inputchannel. A typical application is a differential pressureswitch that senses the pressure drop across a filter bank.When the pressure across the filter bank exceeds the setpointof the differential pressure switch, the Filter status isdisplayed as Dirty on the controller graphic. An alarmindicates a dirty filter.Door SwitchA Door Contact may be configured on any unused binaryinput. A typical application is an occupancy sensormounted within the space served by a single zone rooftop.Door Contact disables mechanical cooling and electric orgas heating, when active. Economizer cooling, ifavailable, continues to operate. A configurable DoorAlarm Delay is provided to prevent immediate action. Thedefault is set to 60 seconds.Remote OccupancyRemote occupancy may be configured on any unusedbinary input channel. A typical application is a remotecontact, controlled by a third party, or an occupancysensor to set the controller’s occupied mode. The RemoteOccupancy function requires both an input configured forRemote Occupancy, and Occupancy Source set to RemoteOcc Input to operate. Once configured, the controller willoperate in the occupied or unoccupied mode, asdetermined by the state of the Remote Occupancy input.LinkageThe RTU Open may serve as an air source to an OpenVariable Volume and Temperature (VVTR) system. Whenthe RTU Open is part of a VVT system and the controllersare wired together to form a network, the controllers mayuse a method of communication known as Linkage. Linkageis a method by which an air source and its subordinate zoneterminals exchange data to form a coordinated HVACsystem. The system’s air source controller, zone controllers,and bypass controller are linked so that their data exchangecan be managed by one zone controller configured as theVVT Master. The VVT Master gathers the followinginformation from the slave zone controllers:S occupancy statusS setpointsS zone temperatureS relative humidityS CO2 levelS damper positionS optimal start dataThe VVT Master performs mathematical calculations andalgorithms on the data and then sends the compositeinformation to the air source. The VVT Master receivesinformation from the air source such as mode, supply airtemperature, and outside air temperature, and passes thatinformation to all linked controllers.Linkage Air Source ModesIn a linked system, the air source determines its operatingmode and qualifies that mode based on its own Supply AirTemperature (SAT). The following modes can be sent bythe air source depending on its configuration:S Off – Air source fan is offS Fan Only – Air source fan is on and providingventilation (neutral SAT) without heating or coolingS Economizer Cooling – Air source fan is on andproviding cooling, using economizer onlyS Cooling – Air source fan is on and cooling is providedby economizer and mechanical coolingS Heating – Air source fan is on and heating is provided(gas or electric)S Dehumidification – Air source fan is on andHumidi--MiZerR is activeS Test – The RTU Open Service Test mode is activeS Shutdown – Air source fan is off due to Safety Chain,Fire Shutdown, or invalid SAT sensorS Unocc Free Cooling – Air source fan is on, with theeconomizer providing cooling while unoccupiedTROUBLESHOOTINGGeneralThe RTU Open controller acts as an intelligent imbeddedthermostat to the rooftop unit, but can be monitored andcontrolled from i--Vu Open (Linkage) or a 3rd partynetwork. This causes the system as a whole to betroubleshot from three points of view. The three parts tothe system are the rooftop unit, the Open controller, andthe network connected. Determining which part needs tobe troubleshot is the first step.The Open controller can be used to troubleshoot the rooftopunit and/or itself with service test, communicating LED’s,and built in alarms. Disconnecting the RTU Open from thenetwork may also help troubleshooting the controller androoftop unit. Third Party Network troubleshooting may alsobe required. For base unit troubleshooting, refer to specificbase unit Service Maintenance manual.There is an on--board battery that is used for RAM andclock back--up (see Fig. 1). It is a 3--volt lithium battery(CR2032). The average life is 7 years with a minimum of10,000 hours of back--up. When the RTU Open board ispowered up, the battery is not being used. If power is lost,the battery backs up the time clock.Replacing the RTU Open’s BatteryTo determine when to replace the battery, remove andmeasure the voltage. If the voltage is below 2.9 volts,replace the battery.48 ---50LHTCQ ---01T