I have discovered a potential design flaw in the motor start capacitor switch on the 6 Hp vertical 30 gallon Crafstman compressor model 919.167310. The motor part number is Z-D23360.
I have had this compressor for less than 3 years and it began to balk when the motor tried to kick on. It would trip a 20 amp breaker in a second or two. I could play with the switch and luck out on occasion and the motor would start and continue to run just fine right up to max pressure. (this took many trips to the breaker panel) S-e-a-r-s would only sell me a new ($166) motor but I knew this sounded like a start capacitor problem. I located a capacitor at Grainger for $5 and tried it but no luck.
So I started to diagnose the system and found that there is a spring loaded cut-out switch in the capacitor circuit. It has a nylon plastic lever that rides against a round phenolic disk on the armature shaft of the motor. There is a spring loaded gentrifugal governor device that moves the phenolic disk and opens the switch once the motor is running. At rest the disk depresses the lever and closes the circuit. Once running the disk backs away from the lever of the switch and allows the contacts to open. That is how it supplies current through the capacitor only upon startup. Since you cannot see this happening with the motor assembled I took measurements and discovered that the lever was not being depressed enough at rest to close the capacitor circuit. It seems that the phenolic disk had worn a slight groove in the lever and caused the switch contacts to only close intermittently or not at all.
There is at least 3/8 inch travel of the phenolic disk and 1/4 inch travel on the switch lever, yet it appears to be designed so that the lever is depressed less than 1/16 at best when the unit was new (I'm guessing).
I remedied this problem easily. The switch plate is screwed onto two bosses in the motor cover. I added two thin washers between the plate and each of the bosses, bringing the switch assembly about 1/16 closer to the phenolic disk. Now the motor starts just fine and I have a spare capacitor for my troubles.
I am a mechanical engineer by trade and I can tell you that this is a design flaw. First of all this is a blind assembly. There is no way for the manufacturer of this motor to verify the amount of lever travel when the cover is assembled to the motor.
This design relies on these variables to work properly:
1. For the phenolic disk assembly to be installed in a precise location on the shaft.
2. For the height of the top of the plastic bosses to be a repeatable distance from the top lip of the molded plastic cover.
3. For the rim of the phenolic disk to be a precise distance from the cast housing that the plastic cover sits on.
4. For the many stamped and crimped metal parts to be installed precisely in the switch plate to determine the exact hieght at which the electrical contacts will touch.
5. For there to be no wear on the nylon lever surface that rides on the rim of the phenolic disk.
This is a tolerance stack-up nightmare that should not have been put into production. The switch plate should have been affixed to the cast metal housing for a more accurate reference to the phenolic disk and most importantly so the operation and travel of the switch could be verified during assembly.
Sorry to get so technical but I have a lot of time on my hands seeing that this problem has blown a car repainting job in the one weekend I had set aside for it. Hopefully the motor manufacturer has corrected this since I bought mine. If not, then hopefully this will save somebody from spending $166 for something that a few cents worth of washers will fix.
If anyone wants pictures or more info let me know. (that includes you S-e-a-r-s guys)
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