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Old 01-26-2013, 11:55 PM
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1idejim 1idejim is offline
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Join Date: Jul 2009
Location: State of Jefferson
Posts: 7,129
Why 24vac won't actuate a solenoid

Quite a few times i see a post where the OP states that he has 24 volts but the solenoid won't work.

I always ask the same few questions, what is the resistance of the wire path and solenoid and what short to earth is.

I took a call from a friend in Texas this week, 24 vac, but he also had 180 ohms resistance from the controller.

Most troubleshooters will begin fooling with the splices because that's what we're taught.

Before i look at anything i will take a short to earth measurement to test the wire insulation. If the insulation is good i look at the splices, if the insulation is bad i grab the A-frame.

Most solenoids require 300mA - 500mA inrush to lift the plunger. That's 7 - 12vA.

Using Ohms law you can see why the valve won't open.


There are 24vA in one Amp. 1A/24vac = 0.041667mA or 1vA.

0.133333/0.041667 = 3vA, less than half the current required to magnatize the coil and lift the plunger.

Electrical troubleshooting can be made a lot easier by doing a little more testing and a lot less guessing.

Hope this helps someone.
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