Does anyone know how to de-magnetize metal? - PeachParts Mercedes-Benz Forum

#1 07-03-2002, 07:47 AM

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

dpetryk · #2 07-03-2002, 08:37 AM

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.

Kestas · #3 07-03-2002, 08:50 AM

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.

dpetryk · #4 07-03-2002, 09:12 AM

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.

#5 07-03-2002, 02:15 PM

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. That’s 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