crankshaft seal is bathed in lubricating oil at a pressureequal to the suction pressure of the refrigerant. The firstindication of crankshaft seal failure is excessive oilleaking at the shaft.When the seal must be replaced or when it showssigns of abnormal wear or damage to the runningsurfaces, a definite reason can be found for the abnormalconditions. Make an inspection to locate and correct thetrouble, or the failure will recur.Seal failure is very often caused by faultylubrication, usually because of the condition of thecrankcase oil. A dirty or broken oil seal is generallycaused by one or both of the following conditions:- Dirt or foreign material is in the system or systempiping. Dirt frequently enters the system at the time ofinstallation. After a period of operation, foreign materialwill accumulate in the compressor crankcase, tending toconcentrate in the oil chamber surrounding the shaftseal. When the oil contains grit, it is only a matter of timeuntil the highly finished running faces becomedamaged, causing failure of the shaft seal.- Moisture is frequently the cause of an acidcondition of the lubricating oil. Oil in this condition willnot provide satisfactory lubrication and will causefailure of the compressor parts. Use a refrigerantdehydrator when the compressor is put into operation ifyou suspect that moisture may be a problem. Anytimeforeign material is found in the lubricating oil,thoroughly clean the entire system (piping, valves, andstrainers).REMOVING A SHAFT SEAL.—If a shaft sealmust be removed, proceed as follows:If the seal is broken to the extent that it permitsexcessive oil leakage, do NOT attempt to pump therefrigerant out of the compressor. If you do, aircontaining moisture will be drawn into the systemthrough the damaged seal. Moisture entering therefrigerant system may cause expansion valves tofreeze. This can cause acid formation and otherproblems. If oil is leaking excessively, close thecompressor suction and discharge valves and relieve thepressure to the atmosphere by loosening a connectionon the compressor discharge gauge line.Next, drain the oil from the compressor crankcase.Since the oil contains refrigerant, it will foam whilebeing drained. Leave the oil drain valve or plug openwhile you are working on the seal. This ensures thatrefrigerant escaping from the oil remaining in thecrankcase will not build up pressure and blow out theseal while it is being removed.Remove the compressor flywheel (or coupling) andcarefully remove the shaft seal assembly. If theassembly cannot be readily removed, build up a slightpressure in the compressor crankcase. To do this,slightly open the compressor suction valve. Take thenecessary precautions to support the seal and to preventit from being blown from the compressor and damaged.INSTALLING A SHAFT SEAL.—Clean andreplace the entire seal assembly according to themanufacturer’s instructions.Wipe the shaft clean with a linen or silk cloth; donot use a dirty or lint-bearing cloth. Be careful not totouch the bearing surfaces with your hands as youunwrap the seal. Rinse the seal in an approved solventand allow it to air-dry. (Do NOT wipe the seal dry!) Dipthe seal in clean refrigerant oil. Follow the instructionsfound in the manufacturer’s technical manual to insertthe assembly. Bolt the seal cover in place and tighten thebolts evenly. Replace the flywheel and belts or couplingand check and correct the motor and compressor shaftalignment. To test the unit for leaks, open the suctionand discharge valves and use a halide leak detector.Evacuating the CompressorWhenever repairs to a compressor allow anyappreciable amount of air to enter the unit, thecompressor should be evacuated after assembly iscompleted and before it is ready for operation Theproper procedure is as follows:1. Disconnect a connection in the compressordischarge gauge line between the discharge line stopvalve and the compressor.2. Start the compressor and let it run until thegreatest possible vacuum is obtained.3. Stop the compressor and immediately open thesuction stop valve slightly. This will blow refrigerantthrough the compressor valves and purge the air abovethe discharge valves through the open gauge line.4. Close the discharge gauge line and open thedischarge line stop valve.5. Remove all oil from the exterior of thecompressor.6. Test the compressor joints for leakage using thehalide leak detector.5-5
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