contaminants). If the oil pressure is high, make necessary repairs to return the oil pressure to engine specification
and proceed to the next paragraph.
Oil return to the engine should not be in any way restricted. Restrictions present in the oil drain connection from
the compressor to the engine can cause a build up of oil in the compressor crankcase sump and increased oil
passing. There is no easy method to measure the quantity of oil drain back or to monitor crankcase oil level. By
design the amount of drain back to the engine should be sufficient under most circumstances.
Areas to check to make sure the oil drain is as efficient as possible are:
• For flange mounted compressors internally drained back to the engine, it is important that the drain ports are
aligned and not restricted by gasket or sealant used during the compressor installation.
• For compressors with external drain lines check for excessive bends, kinks and restrictions in the oil return
line. Minimum recommended oil return line size is 1/2” I.D. (12.7mm). Return line must constantly descend
from the compressor to the engine crankcase.
If restrictions in the drain back system are found make appropriate repairs.
If oil pressure and oil return are found to be OK or repairs were made, proceed to Step 7.
Step 7: Engine Operation
Engine power angle and tilt can affect oil drain back from the compressor on flange mounted applications. These
angles cause the drain to be higher than a portion of the crankcase resulting in the trapping of oil below the drain
level. During operation the piston rods dip into the trapped oil and carry the oil to the cylinder walls. The
increased amount of oil on the cylinder walls results in more oil migrating past the piston rings. TF-750
compressors are more susceptible to this condition because they have longer strokes. If the vehicle is equipped
with a TF-750 compressor and thus far the cause for excessive oil passing has not been found install a bottom
drain cover. If either the engine power angle or tilt is excessive, add a bottom drain to the compressor and place
vehicle back into service.
Check the engine crankcase pressure with a test gauge and compare the reading to engine specifications.
Excessive engine crankcase pressure can cause oil to be forced pass the piston rings increasing oil passing. If
excessive pressure is found repair the cause of the excessive pressure and place vehicle back into service.
If engine power angle and tilt are not causing flooding or the compressor is already bottom drained and engine
crankcase pressure is within specifications proceed to Step 8.
Step 8: Compressor Replacement
Replace the compressor only after reviewing all items in each of the preceding steps.
(49 paginas)
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