Thermostatic Expansion Valves (TXV) — Model 30GTN,R and 30GUN,R 040-110 units are available from the factory with conventional TXVs with liquid line solenoids. The liquid line solenoid valves are not intended to be a mechanical shut-off. When service is required, use the liquid line service valve to pump down the system.
NOTE: This option is not available for modular units.
The TXV is set at the factory to maintain approximately 8 to 12° F (4.4 to 6.7° C) suction superheat leaving the cooler by metering the proper amount of refrigerant into the cooler. All TXVs are adjustable, but should not be adjusted unless abso- lutely necessary. When TXV is used, thermistors T5, T6, T7, and T8 are not required.
The TXV is designed to limit the cooler saturated suction temperature to 55 F (12.8 C). This makes it possible for unit to start at high cooler fluid temperatures without overloading the compressor.
Compressor Protection Control System (CPCS [CPCS — Standard on Sizes 080-110 and Optional on Sizes 040-070]) or Control Relay (CR) — 30GTN,R and 30GUN,R 040-110 — Each compressor has its own CPCS module or CR. See Fig. 13 for CPCS module. The CPCS or CR is used to control and protect the compressors and crankcase heaters. The CPCS and CR pro- vide the following functions:
•compressor contactor control/crankcase heater
•crankcase heater control
•compressor ground current protection (CPCS only)
•status communication to processor board
•high-pressure protection
One large relay is located on the CPCS board. This relay controls the crankcase heater and compressor contactor, and also provides a set of signal contacts that the microprocessor monitors to determine the operating status of the compressor. If the processor board determines that the compressor is not oper- ating properly through the signal contacts, it will lock the com- pressor off by deenergizing the proper 24-v control relay on the relay board. The CPCS board contains logic that can detect if the current-to-ground of any compressor winding exceeds
2.5amps. If this condition occurs, the CPCS shuts down the compressor.
A high-pressure switch is wired in series between the MBB and the CR or CPCS. On compressor A1 and B1 a loss-of- charge switch is also wired in series with the high-pressure switch. If the high-pressure switch opens during operation of a compressor, the compressor will be stopped, the failure will be detected through the signal contacts, and the compressor will be locked off. If the lead compressor in either circuit 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 the ground current circuit protection is not provided.
Compressor Ground Current Protection Board (CGF) and Control Relay (CR) — The 30GTN,R and 30GUN,R 130-210, and associated modular units (see Table 1) contain one compressor ground current pro- tection board (CGF) (see Fig. 14) for each refrigeration circuit. The CGF contains logic that can detect if the current-to-ground
of any compressor winding exceeds 2.5 amps. If this occurs, the lead compressor in that circuit is shut down along with oth- er compressors in that circuit.
A high-pressure switch is wired in series between the MBB and the CR. On compressor A1 and B1 a loss-of-charge switch is also wired in series with the high-pressure switch. The lead compressor in each circuit also has the CGF contacts described above. If any of these switches open during operation of a com- pressor, the CR relay is deenergized, stopping the compressor and signaling the processor at the MBB-J9 inputs to lock out the compressor. If the lead compressor in either circuit is shut down by high-pressure switch, compressor ground fault, oil pressure switch, or the loss-of-charge switch, all compressors in that circuit are also shut down.
Fig. 13 — Compressor Protection Control
System Module — Sizes 040-110
Fig. 14 — Compressor Ground Fault Module
—Sizes 130-210
