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air compressor motor #10546 06/14/02 10:06 PM
Joined: Sep 2001
Posts: 3
maintelec Offline OP
Junior Member
Hi guys i love this site superb mature super guys anyway i have a sears 3 h.p air compressor that wont start under load? you can uncouple the belt and it runs? The start switch is working checked it with a amprobe and the start capacitor has been changed.i disassembled the motor cleaned and checked the bearings? this one has me stuck?? the motor has no data plate which is illegal i thought the tank has 3 h.p. but it has a 16 gauge cord.p s when it loads down it emits a high pich sqeel? thanks in advance?

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Re: air compressor motor #10547 06/14/02 10:23 PM
Joined: Apr 2002
Posts: 21
jo Offline
maybe the start windings in the motor are shot or the belt is to tight

Re: air compressor motor #10548 06/14/02 10:54 PM
Joined: Mar 2001
Posts: 333
stamcon Offline
Is the head unloader working?

Re: air compressor motor #10549 06/15/02 03:41 AM
Joined: Jun 2001
Posts: 29
Resistor Offline
If your sure the motor is ok. It's probably water or oil in the cylinder. Can't compress fluid.

Re: air compressor motor #10550 06/15/02 09:26 AM
Joined: Nov 2000
Posts: 2,236
sparky66wv Offline
No offense, there resistor, but some fluids are very compressable, air for instance. It is liquids that do not compress.

But we knew what you meant...

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Re: air compressor motor #10551 06/15/02 10:05 AM
Joined: Jun 2001
Posts: 29
Resistor Offline
No offense taken WV, but air (pneumatics) is considered gas. No, fluid is not considered compressable (Hydraulics). Unless maybe NASA came out with something new.

Sorry WV, fluid-liquid, your right after all.

[This message has been edited by Resistor (edited 06-15-2002).]

Re: air compressor motor #10552 06/15/02 12:35 PM
Joined: Sep 2001
Posts: 806
NJwirenut Offline
I would check the unloader valve on the compressor first. This valve vents the output from the compressor until the motor gets up to speed, reducing the starting torque required.

Other possibilities include low line voltage, or excessive voltage drop in the line cord.

Re: air compressor motor #10553 06/15/02 08:58 PM
Joined: Sep 2001
Posts: 3
maintelec Offline OP
Junior Member
thanks i have tried bigger cord ,uncouple 2 lines from compressor to tank i am not sure where the unloader is? How can sears advertise a 3 h.p motor that only pulls a few amps and has a #i6 cord.It must me the rating at the compressor end?i can rotate the compressor by hand.It is a used unit and looks to be a few years old/ thanks guys i am gonna try again .

Re: air compressor motor #10554 06/15/02 10:07 PM
Joined: Apr 2002
Posts: 197
Gwz Offline

Get a copy of the UL White Book and under " ELECTRICAL EQUIPMENT FOR USE IN ORDINARY LOCATIONS ( AALZ ) then look for the "Size and Rating" text.

Usually the first couple of numbered pages in the White Book.

It gives a hint that you can not believe all the labeling data on a nameplate.


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