York D*SC360 Installation Instructions Manual

Contents

York D*SC360 Installation Instructions Manual Manual pdf 23 page image

CRANKCASE HEATERSIt is important that the crankcase heaters be energized 8 hoursbefore starting the compressors. To energize the crankcaseheaters, the room thermostat or status panel system switchmust be open to prevent the compressor from starting. If adisconnect switch is installed outside the unit, turn it to “ON”.The nonfused disconnect (optional) located in the unit’s mainsupply panel must also be turned “ON”.CAUTION: Do not attempt to start the compressors without atleast 8 hours of crankcase heat or compressordamage will occur.SAFETY AND SERVICE FEATURESThe control circuit includes the following safety features:1. The supply air blower motor is protected with manual resetstarter overload protectors.2. The condenser fan motors have inherent protection withautomatic reset.3. The primary winding of transformer 1T is protected by fuse12FU. The secondary winding and the 115 volt controlcircuit are protected by fuse 13FU.4. All safety controls in the 115 volt circuit have the “return” or“common” side of the 1T transformer grounded. Fuse 13FUwill “BLOW” whenever a dangerous condition occurs. Theunit casing is also grounded.5. The wiring to each compressor motor, each condenser fanmotor and the supply air blower motor are individually fusedaccording to the National Electrical Standards.6. The compressor(s) are protected by a 100 watt immersiontype crankcase heater(s). Heater(s) are energized when-ever power is supplied to the unit. When the compressor(s)are energized, the heater(s) are turned off.CAUTION: Do not attempt to start the compressors without atleast 8 hours of crankcase heat or compressordamage will occur.7. Each refrigeration system has a low pressure cutout (1LPfor system No. 1 and 2LP for system No. 2) to shut downthe compressor due to loss of refrigerant charge or a buildup of frozen condensate on the compressor before thesuction valve and are set to open when the suction pressuredrops to 7 psig. These controls will automatically reset whenthe suction pressures rise to 22 psig. The opening of thelow pressure cutouts will activate the lockout circuit.8. High pressure cutouts (1HP for system No. 1 and 2HP forsystem No. 2) are located in each system on the compres-sor before the discharge valve. Should a system dischargepressure exceed 398 psig, the control will open and de-en-ergize the compressor. The pressure cutout will close whenthe discharge pressure drops to 310 psig. The opening ofthe high pressure cutout will activate the lockout circuit. Thehigh pressure cutouts may open due to a dirty or restrictedcondenser coil, loss of air flow or too high an ambient airtemperature.9. The lockout circuits mentioned above will not be energizedduring normal operation because they have a high resis-tance. The flow of electricity will normally follow the path ofleast resistance through the compressor contactors 1M and2M. If, however, a low or high pressure cutout opens, thelockout relay 10R or 11R will be energized. Since thevoltage across 10R or 11R will exceed 100V, the voltageacross 1M or 2M will be too low to pull in the contactors.The normally closed contacts of 10R or 11R will open thecircuit in series with the low or high pressure cutout. Whenthese contacts automatically close, the lockout circuit canbe reset by interrupting the control circuit at the roomthermostat. Two advantages are gained by this circuit:a. Prevents rapid cycling of the compressors which can bedamaging.b. The alternate use of manual reset cutoffs avoids theproblem above but may require an expensive servicecall to reset these controls.10. Freezestat 3TH senses the suction temperature of the No.1 system and will shut down compressor(s) when thistemperature drops to 32ÉF. It will reset automatically at37ÉF11. The supply air flow must be proven by vacuum switch 5LP.In the event the belts on the supply air motor break or thesupply air motor should be de-energized by its oveloadprotectors, 5 LP will open and interrupt the cooling, heatingand economizer control circuits. This assures that thevarious modes of operation do not continue without properair flow.12. The compressor motor protector(s), 1MP, 2MP will interruptthe compressor control circuit when sensing an overloadcondition. Also an anti-recycle timer is part of this device toprevent the compressor from rapid cycling. The compressorwill stay off for five minutes. It also monitors the voltage ofthe 120 volt control circuit and will shut down thecompressor if the voltage drops below 85 æ4.5 volts.13. Oil pressure control switches are installed in the compres-sor circuits. These assure that adequate oil pressure ispresent to lubricate the moving parts of the compressor. Ifpressure is not adequate, the switch opens shutting downthe compressor. It is manually reset.14. When the pumpdown accessory, Model 2PD04700101, isinstalled, the compressor will continue to operate throughcontact 12TR-2 after the room thermostat or controller issatisfied.Solenoid 3SOL in the liquid line is now closed and thecompressor pumps most of the refrigerant out of the evapo-rator to the high side of the system. The system suctionpressure drops until the low pressure cutoff (1LP) opens.This will shut down the compressor and de-energizes the12TR relay which opens 12TR-2 to put the operation of thecompressor under the control of the 1R relay. Also presentis a 12TR-1 contact which is closed when the system is offand provides a bypass circuit to allow contactors 1M and2M to be activated in the event the low pressure cutout hasnot reset. Without this pumpdown circuit, it is possible tohave the oil pressure switch (OP/PS) open on light load andshort cycle of the compressor. Refrigerant floods back tothe compressor on each start-up, foams the oil in thecompressor crankcase and pumps the oil to the conden-sate coil. The run times are too short to bring the oil backSTART-UP530.25-N3YUnitary Products Group 23

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