Carrier 48FK Controls Operation And Troubleshooting

Carrier 48FK Controls Operation And Troubleshooting Manual pdf 36 page image

SIZE 044 UNITS — These units have 2 compressors and 1unloader on compressor no. 1. See Fig. 42 for compressorand condenser fan motor locations. The unit operating se-quence is as follows:Stage 1 Relays K1 and K3 are energized. Compressorno. 1 starts with the unloader energized. Com-pressor no. 1 is running at 1⁄ 2 capacity. The crank-case heater on compressor no. 1 has been deen-ergized, and the first stage condenser fan has beenenergized. Outdoor (condenser) fan motor no. 1(OFM1) has started.Stage 2 Relay K1 is energized. Compressor no. 1 is fullyloaded.Stage 3 Relays K1, K3, and K5 are energized. Compres-sor no. 1 is running at 1 ⁄2 capacity, and compres-sor no. 2 is running at full capacity. The crankcaseheater for compressor no. 2 is deenergized. Thesecond stage condenser fan has been energized.Both OFM1 and OFM3 are operating.Stage 4 Relays K1 and K5 are energized. Both compres-sors are running fully loaded.Size 044 units have one fan that can be controlled by theprocessor. The other 2 are controlled by the compressors.The OFM1 is energized by compressor no. 1, and OFM3 isenergized by compressor no. 2. The OFM2 is cycled by theprocessor based on input from either circuit (thermistors T3and T4).SIZE 104 UNITS — These units have 4 compressors and1 unloader on compressor no. 1. See Fig. 43 for compressorand condenser fan motor locations. The unit operating se-quence is as follows:Stage 1 Relays K1 and K3 are energized. Compressorno. 1 starts with unloader energized. Compressorno. 1 runs at 2 ⁄3 capacity. The crankcase heater forthis compressor has been deenergized, and first stageof condenser fans has been energized. Outdoor (con-denser) fan motor no. 1 (OFM1) and oudoor fanmotor no. 3 (OFM3) have started.Stage 2 Relay K1 is energized. Compressor no. 1 is fullyloaded.Stage 3 Relays K1, K3, and K5 are energized. Compres-sor no. 1 runs at 2⁄ 3 capacity and compressorno. 2 is running at full capacity. The crankcaseheater for compressor no. 2 is deenergized. Thefirst stae of condenser fans on circuit 2 has beenenergized. Fans OFM1, OFM2, OFM3, and OFM4are operating.Stage 4 Relays K1 and K5 are energized. Both compres-sors no. 1 and no. 2 are running fully loaded.Stage 5 Relays K1, K3, K5, and K5 are energized. Com-pressor no. 1 runs at 2⁄ 3 capacity and compressorsno. 2 and no. 4 are running at full capacity. Thecrankcase heater on compressor no. 4 is deener-gized. Fans OFM1, OFM2, OFM3, and OFM4 areoperating.Stage 6 Relays K1, K5, and K6 are energized. Compres-sors no. 1, no. 2, and no. 4 are running fully loaded.Stage 7 Relays K1, K2, K3, K5, and K6 are energized.Compressor no. 1 runs at 2 ⁄3 capacity and com-pressors no. 2, no. 3, and no. 4 are running at fullcapacity. Fans OFM1, OFM2, OFM3, and OFM4are operating. Crankcase heater for compressorno. 3 is deenergized.Stage 8 Relays K1, K2, K5, and K6 are energized. Com-pressors no. 1, no. 2, no. 3, and no. 4 are runningfully loaded.On Size 104 units, the first 4 condenser fans energize withthe compressors; circuit no. 1 compressors control OFM1and OFM3, and circuit no. 2 compressors control OFM2 andOFM4. The OFM5 and OFM6 are staged by the micro-processor based on condensing temperature input fromeither circuit’s T3 or T4 thermistor.Head Pressure Control — All units have as standarda basic head pressure control function which allows the unitsto operate in cooling down to 45 F. If cooling is required atoutdoor ambient temperatures lower than 45 F, refer to ac-cessory head pressure control literature for details.Head pressure control is handled by the processor. Theprocessor attempts to maintain the head pressure by cyclingthe condenser-fan motors. No condenser fans will be run-ning without a call for mechanical cooling. Thermistors T3and T4 provide the condensing temperature information tothe processor. These VAV rooftop units have dual refrigera-tion circuits, and the higher circuit temperature will governunit operation. If the condensing temperature is above133 F (236 psig), a condenser fan stage will be added. If thecondensing temperature is 78 F (142 psig) or less, the num-ber of condenser fans operating will be decreased. After eachfan stage, the processor will wait one minute for the headpressures to stabilize before changing again, unless ther-mistor T3 or T4 senses a temperature greater than 125 F(278 psig), in which case all condenser fans are started.During start-up, if the outdoor ambient is above 70 F (assensed by thermistor T3 or T4), the first-stage, processor-controlled fans are turned on to prevent excessive dischargepressures.034 AND 038 UNITS 044 AND 048 UNITSLEGENDOFM — Outdoor (Condenser) Fan MotorFig. 42 — Component Arrangement, 034-048 Units36