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current in vehicle's AC ON/Off switch

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Full Member level 5
Nov 28, 2009
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hi friends, I want to sense vehicle AC on/off using microcontroller. I can do it by sensing the on/off switch available in every AC. But what about the current? how much current flows through this switch when ON.I cannot connect it to micocontroller.Any idea?

thanks in advance.

The AC switch carries current to the fan, and to vent actuators, and to activate a release of some kind on the compressor brake so it will spin under engine power. I believe I've seen or heard the compressor turn off and on with at least one car, so I think there's a relay involved.

So I don't know how much current the wire to the switch carries...


If you wrap several turns of wire around it, you'll get some kind of inductive spike through it. One spike when you turn on AC, and another when you turn it off.

The greater the current being switched, the greater the spike. One polarity when turned on, the opposite polarity when turned off.

You'll get no reading from the coil between those times.


There's also the concept behind the clamping current meter that has jaws which you clamp around a wire. Don't know how easy it would be to adapt for your purpose. I imagine it uses a hall-effect sensor.


There's also a meter called an 'inductive' meter but the needle is really attached to a magnet. I've seen it carried by JC Whitney automotive supply. You simply hold it next to a wire. The greater the current flowing, the more the needle deflects. It barely moves when one amp is flowing. This action is observable by eye but hard to measure electronically.


There's such a thing as an inductive proximity sensor. Cost can be $50 or more. Don't know whether it does what you're asking but for that kind of money it should be able to do things inexpensive hobby parts can't do.
Usually, a magnetic clutch is activating the compressor. It should consume a few amps. A current relay, e.g. formed by a reed contact with a coil, can be used to sense the current. Probing the switched voltage would be still the most easy way.

An inductive proximity sensor has nothing to do with current measurement. As the name reveals, it senses proximity (of metal parts).
Can you show me some diagram.
thanks for the reply

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