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?

maybe the start windings in the motor are shot or the belt is to tight

Is the head unloader working?

If your sure the motor is ok. It's probably water or oil in the cylinder. Can't compress fluid.

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...

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).]

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.

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 .

maintelec,

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.