Carrier 48HG014 Controls Operation And Troubleshooting

Contents

Carrier 48HG014 Controls Operation And Troubleshooting Manual pdf 28 page image

28Power Exhaust — To enable power exhaust, PE.ENmust be set to YES. If power exhaust is enabled, PowerExhaust 1 will turn on when the economizer position is greaterthan PE1.P. If power exhaust is enabled, Power Exhaust 2 willturn on when the economizer position is greater than PE2.P.There are small time delays to ensure that rapid cycling doesnot occur.Compressor Staging — The electronic controls deter-mine the number of cooling stages needed at any given timeas specified in the Cooling section. However, which specificcooling stage operates at any given time depends on compres-sor staging order and compressor status.COMPRESSOR STAGING ORDER — The 48/50HG016-024units have three stages of cooling (Circuits A, B and C).The 48/50HG014 and 028 units have two stages of cooling (Cir-cuits A and B). The position of the evaporators for Circuits A, Band C are bottom, middle and top (see Fig. 4) for a 3-circuit unit.The position of the evaporators is bottom and top for Circuits Aand B on a 2-circuit unit. Depending on conditions listed below,circuits will either stage from the bottom evaporator to the topevaporator (BtoT) or from the top evaporator to the bottomevaporator (TtoB). When the unit is staging TtoB, the unit isstated to be inverted.If inverting is not allowed as determined by the configura-tion (INV.E = NO), the unit will always stage BtoT. However,if INV.E = YES, then the unit will invert if the outdoor temper-ature as measured by OAT is greater than 80 F for 15 minutescontinuously. Inverting will continue until either INV.E is set toNO or the OAT drops below 75 F for 1 minute.COMPRESSOR STATUS — Having determined whetherstaging will occur as either BtoT or TtoB, the unit controls willdetermine the final order of compressor staging. If all circuitsare functioning properly, the compressor staging will alwaysfollow either BtoT or TtoB. Therefore if the staging method isBtoT, then Circuit A must turn On before Circuit B andCircuit B before Circuit C. Likewise when removing stages,the stages must be removed in the opposite order. In all cases,the minimum on-time of 3 minutes (MRT.C) and the minimumoff-time of 5 minutes (MOT.C) must be honored. Therefore, ifthe staging order is BtoT and Circuit A was shut down twominutes previously, no circuits will turn on until the minimumoff-time for Circuit A has expired; no matter how many circuitsare requested.The rules are different if a circuit has shutdown because ofan alarm such as low refrigerant pressure. When a circuit is un-available because it is not functioning properly, it will be re-placed immediately by another circuit. Therefore, if Circuit Aand B are operating because two circuits have been requested,the staging is BtoT, and then Circuit A shuts down because oflow refrigerant pressure, the control will turn off Circuit A andreplace it with Circuit C. Later if Circuit A is allowed to restart(see Alarm Handling on page 31) and BtoT is still active withtwo requested stages, Circuit A will attempt to restart. If CircuitA has run for 1 minute without sensing any problems, it will bedeemed acceptable, causing Circuit C to shutdown. Circuit Cwill shut down because only two circuits are needed andCircuit A and B are functioning properly.Heating (48HG Units)NOTE: THE 48HG units have 2 stages of heat.For 48HG units, the heat type will automatically be set to 1for gas units (HT.TY). Heat will not operate if the outdoor tem-perature is greater than the heat lockout temp (HT.LO).THERMOSTAT CONTROL — When the thermostat callsfor heating, the MBB senses that W1 is On and closes theHTR.1 relay. When the relay is closed, it sends power to W onthe IGC (integrated gas unit controller) board. An LED (light-emitting diode) on the IGC board will be on during normaloperation. A check is made to ensure that the rollout switch andlimit switch are closed. The induced-draft motor is thenenergized. When speed is proven with the Hall Effect sensor onthe motor, the ignition activation period begins.100500 7001100INSIDE/OUTSIDE CO2 DIFFERENTIALINSIDE CO2 CONCENTRATIONAQDIFFERENTIALLOW (AQD.L)AQDIFFERENTIALHIGH (AQD.H)MINIMUMIAQDAMPERPOSITION(AQ.MP)ECONOMIZERMINIMUMDAMPERPOSITION(MIN. P)INCREASING VENTILATIONVENTILATION FOR PEOPLEVENTILATION FOR SOURCESFig. 12 — IAQ Control202→