Carrier 48FC Series Controls, Start-up, Operation And Troubleshooting

Also see for 48FC 04: Installation instructions

Carrier 48FC Series Controls, Start-up, Operation And Troubleshooting Manual pdf 34 page image

34Control Module CommunicationRed LEDProper operation of the MBB control board can be visuallychecked by looking at the red status LED. When operatingcorrectly, the red status LED should blink at a rate of once every 2seconds. If the red LED is not blinking, verify that correct power isbeing supplied. A blinking red LED at the rate of once per secondmeans that software is not loaded on the board. Also, be sure thatthe board is supplied with the current software. If necessary, reloadcurrent software. A board LED that is lit continuously should bereplaced.Green LEDThe MBB has one green LED. The Local Equipment Network(LEN) LED should always be blinking whenever power is on. IfLEN LED is not blinking, check LEN connections for potentialcommunication errors (MBB J15, J16, J17, and on the Display J2).Communication between modules is accomplished by a 3--wiresensor bus. These 3 wires run in parallel from module to module.The MBB J17 and Display J2 connectors provide both power andcommunication directly at the connector for accessories like theNavigatort display. The MBB J15 connector provides a LENinterface to the indoor fan VFD.Yellow LEDThe MBB has one yellow LED which is used to indicate BuildingAutomated System (BAS) communication activity. The LED willblink when the MBB transmits a message on the bus.Communication FailuresIf the Indoor Fan VFD or Navigator display CommunicationFailure or the green or yellow LED’s do not flash on the boardsthen the problem could be the communication chip on one of thecontrol boards (MBB). Use an ohm meter to measure the resistanceon the communication pins of the boards to determine if the boardis bad. If the reading is less then half the value indicated in Table13, then the board needs to be replaced.IMPORTANT: The resistive values should be read when theboard is powered off, the unit is locked out, and boardconnectors are disconnected.Table 13 – Communication ResistancesDevice(LEN) Resistance between Pins /Connector(BAS) Resistance between Pins /Connector(RNET) Resistance between Pins /ConnectorPins1 to 3Pins1 to 2Pins2 to 3Pins1 to 3Pins1 to 2Pins2 to 3PinsGND to +PinsGND to –Pins+ to –MBB 19.92 KΩ 10.63 KΩ 9.51 KΩ 19.92 KΩ 10.63 KΩ 9.51 KΩ 2.25 KΩ 1 KΩ 3.3 KΩ