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azsteve

08:18PM | 11/05/04
Member Since: 11/04/04
12 lifetime posts
Bvtools
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)

Regards,

Steve


SHILOSHEPHERD

04:47PM | 11/10/04
Member Since: 11/09/04
4 lifetime posts
What great research. I am having the same problem and was looking for two capacitors as I thought I mught have blown them but I could not even find those. I did short some wires in a light in the same circuit so I assumed that shorted the capacitor but your idea is better to start off with and paid for with a lot of frustration. I'm a bit lost on where this is so if you could send some pics that would be great!! If you know where to get capacitors (one is a Mallory and the other a CSC)but those numbers are hard to locate. This was a two stage professional but it is a couple years old and only actually run for 10 minuites max before it started humming rather than starting. I shut it down rather than trip. I'm assuming this lever is inside the motor so that will be a bit over my head but we shall see. Thanks!! [email protected] is my address.

SHILOSHEPHERD

09:13PM | 11/12/04
Member Since: 11/09/04
4 lifetime posts
I found the courage to open up the motor on my 2 stage professional. Using AZsteve's description I found on the inside where the wiring connects one little relay on each side that handles each capacitor. One run capacitor and one start capacitor (be carefull with capaitors as they can shock with power off). The relays were too far apart as azsteve had advised. I moved them by bending the stiffest metal support to as close as I could get and still see some light. I assume getting too close could destroy the motor. I was advised that one can normally see burns on a bad capacitor and it can be tested with something like a Simson that will charge the capacitor while measuring resistance (to say 6 volts etc.) and then you can watch it discharge by switching to volts. The battery on the simson does the charging. Both of the capacitors would take charge and discharge this way so they were good. I don't know if this is always true. Poor design and with the precise construction of that plastic case I find it hard to beleive it is just an oversight. It takes small hands a dexterity to hold down the upper bolts on the motor casing without removing the little blower but I was able to do it barely. Not very technical but I hope this saves someone a lot of money. That 15 amp motor listed at $350 so most folks would consider dumping rather than fixing. Good luck and thanks to azsteve.

azsteve

05:51PM | 11/14/04
Member Since: 11/04/04
12 lifetime posts
Shiloshepard,

I have found the root cause and will put together a document with pictures and a "how to" on options to fix the problem. I know what you did to get your unit working but you do risk keeping the motor start capacitor in circuit if the contacts decide to arc. This could do some damage. I will post in a day or so with more info. Please reply and let me know if my email address is available to you in my profile so I can get this info to you.

Regards,

Steve


azsteve

09:49AM | 11/15/04
Member Since: 11/04/04
12 lifetime posts
I was unable to contact the moderator and it does not seem possible to post attachments on this forum, so I will bravely post my email address here if you want photos.

smusante(at)comcastDOTnet

replace (at) with @

replace DOT with .

After receiving responses to this message I decided to dig further into this problem. It bothered me that I saw so little wear on the switch lever. I just could not believe that this unit was designed with such a small margin of operational tolerance. I thought it looked odd that there was a retaining washer on the shaft that was not really performing any function. My hunch was that the centrifugal actuator assembly had originally been out flush with the retaining washer. By pushing on the phenolic disk it was obvious that the disk more or less slams against the back of the assembly when the motor starts. This could create the effect of a slide hammer and possibly move the assembly up the shaft by a tiny increment each time the motor started. I did not want to break any of the plastic parts of the actuator but I had to know for sure so I put a couple of pry tools behind the base of the actuator, and with much less resistance than I expected, the actuator slid forward into the retaining washer.

I was happy to find the root cause of the problem but I was also disappointed by the reality of how rinky-dink this problem is. The actuator assembly consists of a molded glass-filled nylon sleeve and carrier that the springs, weights and phenolic disk are attached to. The assembly itself seems well made. The sleeve is a tight enough press-fit to guarantee that it will spin with the shaft and not slip under starting torque. (normally you would use a keyway to prevent this) All it would take is a snap ring groove and snap ring on either side of this actuator to prevent the actuator from moving on the shaft and make this a long life motor.

Unfortunately the manufacturer opted for cheaper retaining washers to position the assembly on the shaft, and I don't know if they were supposed to use a retainer on the back side of the assembly or not, or if there was supposed to be a spacer sleeve to prevent movement of the assembly. Mine did not have either and I would say that others may have the same problem. If they were all built this way then it is all a matter of how tightly the actuator fits on the shaft. If it is very tight then they may never see a problem.

I also have a theory that the phenomenon of cold flow may be having an influence on this problem. It is a fact that plastics, especially molded thermoplastics, when put under long term compression or tension, can relax, creep, or "cold flow". This means that a sleeve that is pressed onto the shaft at the factory may seem impossible to budge but after a couple of years of use and the high temperatures that the shaft sees may cause the sleeve to become loose enought to start slipping. In this scenario, the more you use the compressor and the higher the the ambient temperature, the sooner the problem will surface. If I am right about this then the secondary problem of the actuator slipping on the shaft may also occur, and would mimic the problem of refusing to start. I see temps above 100 degrees in my garage most of the summer here in Tucson so I am probably experiencing the problem sooner than someone in Minneapolis.

The bottom line here is that we as owners of this fine Crafstman compressor have a fundamental product reliability problem. If you purchased the extended warranty and it is about to expire, then you may want to contact S-e-a-r-s to express your concern about this issue. They MUST know about it by now. Although it is possible to do the quick remedy of sliding the actuator back into position, this may turn out to be a progressive problem and may require more frequent attention if my theory of cold flow holds up. The motor manufacturer has complicated things by using the retaining washer. They are almost impossible to remove without ruining them, and without marring the shaft. A better fix would involve marking the proper location of the actuator on the shaft, removing the retaining washer, completely removing the actuator, roughing up the shaft where the actuator sits, solvent cleaning the shaft and actuator, and installing the actuator on the shaft with a suitable bonding adhesive. The retaining washer would no longer be needed, since it did no good in the first place other than to give us a reference for where the actuator should be.

I hope this all helps.

Steve


mediator

12:37PM | 12/03/04
Member Since: 12/02/04
1 lifetime posts
Hi Steve, Bless you for all your outstanding research and insight into this problem. I have a slightly different model compressor (919.167300) with the same problem. ***** offered me the same $166 solution. Pretty silly for a unit I bought on clearance for $125.00 including a 3/8" wratchet. Upon disassembly there was the unmistakable smell of burnt electrical stuff and I found the motor start capacitor to be smoked. Like you, I'm in the South (South Florida) and my garage is routinely 95 degrees and the compressor is used 3 or 4 times a week. None of the usual places I buy parts has the capacitor in stock so I was Googling on line for it when I stumbled across your research. Could you please send me the picture you are talking about and also the Grainger part number if you have that handy? Thanx so much for your help. my Email is [email protected]

Jeff

azsteve

03:12PM | 12/03/04
Member Since: 11/04/04
12 lifetime posts
Jeff,

The Grainger part number is 4CU32 and is manufactured by CGE. It will set you back a whole $6.07. It should be a perfect fit if your motor is the same as mine.

I'm sending you the instructions with photos.

Steve


azsteve

12:45PM | 04/30/06
Member Since: 11/04/04
12 lifetime posts
As I mentioned in a previous post I have created a document with photos for reference.

Here is the link:

http://www.pro-menu.com/compressor/compressor_fix.pdf

Regards,

Steve


jam890

03:02AM | 03/09/08
Member Since: 03/08/08
1 lifetime posts
Steve or anyone else,

When repairing our compressor, we found the acuator/disk on the motor shaft cracked. Sears will only sell the motor. Any idea where to get one or to buy a defective motor for parts? Thanks for your time.

azsteve

02:04PM | 03/10/08
Member Since: 11/04/04
12 lifetime posts
Sorry but I was never able to find the manufacturer of this particular motor or parts. You might try local compressor repair shops. I will check locally here and post back if I locate anything.
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