Carrier 30GTN Service And Troubleshooting Manual

Also see for 30GTN: Product data Installation instructions Installation instructions

Carrier 30GTN Service And Troubleshooting Manual Manual pdf 15 page image

Thermostatic Expansion Valves (TXV) —Model 30GTN,R040-110 units are available from the fac-tory with conventional TXVs with liquid line solenoids. Theliquid line solenoid valves are not intended to be a mechani-cal shut-off. When service is required, use the liquid line serv-ice valve to pump down the system.NOTE: This option is not available for modular units.The TXV is set at the factory to maintain approximately8 to 12° F (4.4 to 6.7° C) suction superheat leaving the coolerby monitoring the proper amount of refrigerant into the cooler.All TXVs are adjustable, but should not be adjusted unlessabsolutely necessary. When TXV is used, thermistors T5,T6, T7, and T8 are not required.The TXV is designed to limit the cooler saturated suctiontemperature to 55 F (12.8 C). This makes it possible for unitto start at high cooler fluid temperatures without overload-ing the compressor.Compressor Protection Control System (CPCS)or Control Relay (CR) — Each compressor has its ownCPCS module or CR. See Fig. 13 for CPCS module. TheCPCS or CR is used to control and protect the compressorsand crankcase heaters. The CPCS and CR provide the fol-lowing functions:• compressor contactor control/crankcase heater• crankcase heater control• compressor ground current protection (CPCS only)• status communication to processor board• high-pressure protectionOne large relay is located on the CPCS board. This relaycontrols the crankcase heater and compressor contactor, andalso provides a set of signal contacts that the microprocessormonitors to determine the operating status of the compres-sor. If the processor board determines that the compressor isnot operating properly through the signal contacts, it will lockthe compressor off by deenergizing the proper 24-v controlrelay on the relay board. The CPCS board contains logic thatcan detect if the current-to-ground of any compressor wind-ing exceeds 2.5 amps. If this condition occurs, the CPCSshuts down the compressor.A high-pressure switch is wired in series between the MBBand the CR or CPCS. On compressor A1 and B1 a loss-of-charge switch is also wired in series with the high-pressureswitch. If the high-pressure switch opens during operationof a compressor, the compressor will be stopped, the failurewill be detected through the signal contacts, and the com-pressor will be locked off. If the lead compressor in eithercircuit is shut down by the high-pressure switch, loss-of-charge switch, ground current protector, or oil safety switch,all compressors in that circuit are shut down.NOTE: The CR operates the same as the CPCS, except theground current circuit protection is not provided.Compressor Ground Current Protection Board(CGF) and Control Relay (CR) — The 30GTN,R130-210, and associated modular units (see Table 1) contain onecompressor ground current protection board (CGF) for eachrefrigeration circuit. The CGF contains logic that can detectif the current-to-ground of any compressor winding exceeds2.5 amps. If this occurs, the lead compressor in that circuitis shut down along with other compressors in that circuit.A high-pressure switch is wired in series between the MBBand the CR or CPCS. On compressor A1 and B1 a loss-of-charge switch is also included with the high-pressure switch.The lead compressor in each circuit also has the CGF con-tacts described above. If any of these switches open duringoperation of a compressor, the CR relay is deenergized, stop-ping the compressor and signaling the processor at the MBB-J9inputs to lock out the compressor. If the lead compressor ineither circuit is shut down by high-pressure switch, com-pressor ground fault, oil pressure switch, or the loss-of-charge switch, all compressors in that circuit are also shutdown.Fig. 13 — Compressor Protection ControlSystem Module15