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  #1  
Old 07-03-2002, 08:47 AM
PA_Joe_300E
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Does anyone know how to de-magnetize metal?

The shaft on my ac compressor is magnetized. It interferes with the speed sensor and shuts down as soon as the rpm go passed 2K
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  #2  
Old 07-03-2002, 09:37 AM
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Electrons can do anything
 
Join Date: Sep 2001
Location: Houston, Texas
Posts: 1,071
To demagnetize metal follow this proceedure;

1. Using an electromagnet with AC voltage applied, put the metal to be demagnetized on the electromagnet so that a good magnetic circuit or coupling is achieved.

2. Then slowly seperate the electromagnet from the magnetized part.

The constantly reversing magnetic field of the electromagnet will slowly weaken as the distance is increased and the part will be left with a neutral magnetic charge.

From your description of the problem, I doubt that a permanently magnetized shaft is your problem. I would suggest that you are low on freon and the low side pressure switch is causing the compressor to cut off when the pressure is too low which will occur during high RPM and low on freon.
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  #3  
Old 07-03-2002, 09:50 AM
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Join Date: Jun 2002
Location: Motor City, MI
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Are you sure it's the a/c shaft magnetization that's causing the problem? The a/c clutch is a magnetic clutch that would reasonably magnetize the shaft over time. How was this diagnosed? Perhaps the speed sensor is subpar.

If the problem is indeed excessive magnetization of the shaft, there are degaussing units available. If the a/c compressor is out of the car, take it to an automotive machine shop that does magnafluxing. They should have a degaussing unit in the shop. If the a/c is in the car, I can only recommend checking a TV repair house for a portable degausser used on TV picture tubes or an electronics store for degaussers used for tape heads. The ones for tape heads may be too small for what you need, though.
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  #4  
Old 07-03-2002, 10:12 AM
dpetryk's Avatar
Electrons can do anything
 
Join Date: Sep 2001
Location: Houston, Texas
Posts: 1,071
I would like to point out that the speed sensor is on the opposite end of the compressor from the clutch. Any residual magnetic field would have to travel thru the compressor to affect the speed sensor.
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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k
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  #5  
Old 07-03-2002, 03:15 PM
PA_Joe_300E
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Thanks for your ideas on demagnetizing.

The A/C system has been looked at by two different techs and my self. The pressure switch, klima relay, expansion valve, and speed sensor have been replaced. Also the compressor was resealed. I resealed the compressor myself and replaced the speed sensor. Thatís when I noticed the shaft was magnetized. The new speed sensor is not generating the required voltage.

It could be a defective speed sensor... It's a simple design... I can't see it not working. Any Ideas are welcomed. The shaft held strong on my screw driver. I thought it odd at the time
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