Most smaller open drive and some direct drive semi-hermetic compressors employ this type of crankshaft seal. They are often a cause of noise complaints (squeaking) and refrigerant leaks. Generally this is due to lack of lubrication; when the seal surfaces are dry, wear and scoring of the polished facings occur.
In order to remove this type of seal it is necessary first to remove the compressor flywheel. The larger the compressor, the larger and heavier will be the flywheel. Extra care must be exercised when removing the larger types, which may be castings and easily damaged if dropped. Removal should not be attempted without a suitable extractor. Under no circumstances should a hammer be used to break the bond between shaft, keyway and flywheel boss (not for semi-hermetic compressors).
Systems must be pumped down and isolated electrically. The drive belt guards must be removed to gain access to the flywheel on units with water cooled systems or with a remote condenser. On smaller air cooled units the compressor must be removed from its base, and this is dealt with here.
Open drive units (valves in the head type)
1. Pump down the system, front seat both service valves and isolate the unit electrically.
2. Remove the head retaining bolts and gently raise the compressor head.
3. Withdraw the valve plate assembly and remove the suction reeds from the cylinders.
4. Remove the compressor mounting bolts and belt guard.
5. Slide the compressor body towards the drive motor, release the drive belts from the flywheel and remove the compressor body.
6. Release the locking device on the drive shaft. This could be in the form of two locknuts, a locknut and a tab washer, or a locknut and a pin.
7. Using a suitable extractor, locate the arms around the flywheel boss (avoid locating around the flywheel vee section). Never use a hammer to remove a flywheel.
8. Apply gentle pressure on the extractor to break the bond, then remove the flywheel. With large heavy types it is advisable to tie a rope or cord to the flywheel and secure it in case the bond breaks suddenly.
9. Remove the seal plate retainer bolts and seal plate. The seal will be released by spring pressure in most cases; withdraw the seal from the seal housing.
10. Remove the seal ring from the shaft.
It may be necessary to change the compressor oil when a seal replacement is made, or some oil may be lost during replacement.
The procedure for replacement is as follows. Some manufacturers supply a shaft centring tool to ensure that the seal is correctly aligned on the shaft; this also eliminates uneven pressure being applied by the seal plate and spring during assembly.
1. Locate the seal ring on to the shaft and push fully home to the shaft shoulder.
2. Dip the seal nose in refrigeration oil and locate over the shaft, using the centring tool if available.
3. Replace the seal plate, depressing evenly against the spring. Insert the retaining bolts, and tighten the bolts so as to maintain the correct alignment of the shaft seal assembly.
4. Reassemble the compressor, belts etc. in reverse order. Check the belt tensioning and the alignment of the drive option and flywheel.
5. When reassembly is complete, fit gauges if these have been removed to facilitate the replacement.
6. Crack off both service valves from the front seat positions and purge the compressor through the gauge port unions if there is sufficient refrigerant pressure in the system. If the charge was lost, then evacuate, fit a new filter drier, charge the system and check the oil level.
7. Carry out a leak test.
8. Start the plant and check the system operation.
9. Remove gauges.
10. Clean the compressor and clear the site.
Direct drive units
This type of compressor does not have a flywheel or drive belts; the compressor is linked to the drive motor by means of a coupling. To gain access to the seal housing, this will have to be dismantled before the seal plate and seal assembly can be withdrawn. It may also be necessary to move the drive motor in order to remove the seal assembly.