ENGINEMAN 1 & CCapacity Control ValveThe capacity control valve (figure 6-8) islocated in the compressor crankcase cover. Thevalve is actuated by oil pressure from the mainoil pump, and its function is to admit or relieveoil to or from the individual unloader powerelements, depending on suction or crankcasepressure. When the compressor is at rest the twocylinders equipped with the unloader element areunloaded and remain unloaded until the com-pressor is started and the oil pressure reaches nor-mal operating pressure.As the high pressure oil from the pump enterschamber A of the capacity control valve andpasses through an orifice in the top of the pistonto chamber B, it forces the piston to the end ofits stroke against spring A. When the piston ofthe valve is forced against spring A, the circulargrooves which form chamber A are put in con-tact with the unloader connections. This admitshigh pressure oil to the unloader cylinder,actuating the unloader mechanism.To control the oil pressure from the capacitycontrol valve, a capacity control regulatingneedle valve is installed. It is connected to thecrankcase and has an oil connecting line tochamber B of the capacity control valve. As thecrankcase,or suction pressure pulls downslightly below the setting of the regulating valve,the regulator needle valve opens and relieves theoil pressure from chamber B of the capacity con-trol valve. This permits spring A to push thecapacity control piston one step toward chamberB, uncovering the unloader connection nearest theend of the capacity control valve. This actionrelieves the oil pressure from the power elementand allows the power element spring to rotate thecam rings and unload the cylinder.If the suction pressure continues to drop, theregulator needle valve relieves more oil pressureand more cylinders become unloaded. On theother hand, if the heat load increases, the suctionpressure increases, causing the regulating needlevalve to close and more cylinders to becomeloaded.MAINTENANCE PRECAUTIONSIf a compressor cannot be pumped down andis damaged to the extent that it has to be openedfor repairs, it is necessary first to close the suc-tion and discharge valves and then following allsafety precautions, to allow all the refrigerant inthe compressor to vent to the atmosphere througha drain plug.When it becomes necessary to remove, replace,or repair any internal parts of the compressor,observe the following precautions:1. Carefully disassemble and inspect whileremoving all parts, noting their correct relativeposition so that errors will not be made whenreassembling.2. Inspect all parts that become accessibleafter the removal of those parts requiring repairor replacement.3. Make certain that all parts and surfaces arefree of dirt and moisture.4. Apply clean compressor oil freely to allbearing and rubbing surfaces of the parts beingreplaced or reinstalled.5. If the compressor is not equipped with anoil pump, make certain that the oil dipper on thelower connecting rod is in the correct position fordipping oil when the unit is in operation.6. Position the ends of the piston rings so thatalternate joints come on the opposite side of thepiston.7. Take care not to score the gasket surfaces.8. Renew all gaskets.9. Clean the crankcase and renew the oilfollowing correct procedures.EVACUATING THE COMPRESSORIn all but emergency situations it is desirableto evacuate the compressor with a vacuum pumprather than with the compressor itself. However,if you do not have a vacuum pump available, usethe following procedure:1. Disconnect the connection in the com-pressor discharge gage line, between the dischargeline stop valve and the compressor.2. Start the compressor and let it run until thegreatest possible vacuum is obtained.3. Stop the compressor and immediately openthe suction stop valve slightly in order to blowrefrigerant through the compressor valves andpurge the air above the discharge valves throughthe open gage line.6-6
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